Population spatial agglomeration is the basis for the economic growth of urban agglomerations in China. A dynamic panel regression model is established on the basis of the theoretical derivation of the relationship between population spatial agglomeration and economic growth in urban agglomerations. The study has three major findings. (1) The spatial concentration of population in urban agglomerations in China has a significant impact on the economic growth of urban agglomerations. (2) The effect of population agglomeration on economic growth in urban agglomerations is a non-linear “inverted U-shaped” relationship. At the initial stage of population agglomeration, the population agglomeration to the core cities within urban agglomerations is conducive to improving the economic efficiency of urban agglomerations, and after the population agglomeration reaches a certain level, the economic efficiency will be weakened. (3) Industrial structure optimization and technological progress are useful for the economic growth of urban agglomerations. Capitalizing on the urban agglomeration dividend, it is important to reduce the negative externalities of excessive spatial concentration of population in urban agglomerations, thus promoting high-quality development of urban agglomerations.

Based on the data of the 7th Population Census in China, this paper examines the latest situation of the labor force population, including the trends of size and proportion, the ageing of the structure, the spatial agglomeration and the quality of the labor force, analyzes the challenges for the labor market, and discusses policy implications.

Since 2015, the implementation of “The Outline of Beijing-Tianjin-Hebei Coordinated Development Plan” has led to a new thinking of Beijing's population regulations in the new era, based on the measures of relocating non-capital functions of Beijing, promoting the coordinated development of Beijing-Tianjin-Hebei, and driving population decentralization through functional decentralization. This paper evaluates the effectiveness of Beijing's population regulation policy since 2015 by using the quasi-natural experiment of difference-in-differences-in-differences estimation. This paper finds that the implementation of Beijing's population regulation policies is negatively correlated with the size of permanent residents, and the policies effectively reduce the population of permanent residents by 11.6% compared to the case without the new polices. The policy effect becomes significant after 2017 and increases year by year. Further analysis suggests that because the 2020 population planning target has been basically achieved, the population regulation targeted at scale control needs to be adjusted. Under the framework of comprehensive optimization objectives, space optimization and quality improvements of population should be carried out in next step.

Urban population control in China has been carried out for many years，however，there are a number of academic issues associated with the deficiency of basic theories of population control system，which leads to lack of consensus on some basic problems.Based on review and analysis of the literature，this study proposes some thoughts on the domestic urban population regulation through logical deduction and theoretical derivation methods.Regarding the controversy on whether the government should direct in population regulation，this work has identified a number of weakness and limitations of resources in mega cities，which can be caused by the failure of market mechanism，mega-urban diseases，and demographic factors.In fact，the reduction of urban population growth is achieved by government regulation instead of market conduct，which verifies the effect of government regulation in urban population control.Meanwhile，a number of problems that should be noticed have been listed including the diversity of population regulation target (instead of the simple theory of population determinism)，the failure of market mechanism，the coordination of industry layout and population，the avoidance of direct administrative intervention in population regulation，and the legal means in urban governance controls.

 Labor supply is an important source of economic growth．In this paper，we use the factorization method to quantify the contribution of labour supply in China's economic growth by decomposing the labor supply factor into the population size，the proportion of working-age population，and the labor participation rate factors．We put them all into the classic Cobb-Douglas production function．Based on the theoretical model derivation，this paper analyzes the time series data from 1978 to 2015．The results show that labor supply has a significant contribution to China's economic growth in a long term．Its impact and contribution are less significant than the fixed assets，but much greater than the human cap- ital．The main contribution of China's economic growth comes from the input of material capital rather than the labor supply．All of the three variables representing the scale of labor supply have significant effects on economic growth in the same direction，but the magnitude of the effects varies．The order of the contribution and elasticity of the three factors to the total economic output are the total population，the proportion of the working-age population，and the labor participation rate．Finally， in recent years the decrease of the proportion of working-age population does suppress China's economic growth，but this negative impact is to some extent offset by the increase in the size of the total population．

The optimum population under the constraint of resources and environment，by which both the con- straints of resources and the environment are met and a certain standard of living and development goals are achieved，is an important basis for China’ s future population policy considerations．Based on the concept of optimum population and the analysis of its internal mechanism under the constraint of resources and environment，12 indexes are selected from the fields of natural resources，environmental and socioeconomic development．Using the possibility- satisfiability model，we separately estimate the optimum scale of China’ s population under a single factor and different combinations of indexes in both 2030 and 2050 as the target point time．The results show that the lowest value of China’ s optimum population under the constraints of major resources and environment is around 1157-1322 million in 2030 and 1465-1626 million in 2050，while the desired optimum population of China would be 986-1311 million in 2030 and 1188-1389 million in 2050． Water resource is always the most important factor in restricting China’ s population growth in the future．The relationship between population，resources and environment would be more strained by 2030，and then would tend to improve after 2050．

This paper examines the destination choice of migrants from a cost-benefit perspective, using binary logit models to explain why the megacities are so popular to be their destination. The results show that the net revenue, particularly different wage levels the floating individuals expect has great impact on their destination choices, which validates an important fact that high-wage income or that the huge wage gap between different regions is an important reason why migrants flowing into megacities. The total expenditure of floating migrants in Beijing, Shanghai and Guangzhou does not inhibit their flowing into these large cities. Implications of the results are that rather than taking measures to raise the cost of living in the cities to limit the floating population, it is better to make efforts in developing neighboring regions to attract more enterprises, create more jobs, and improve public services, thus redirecting the migrants in choosing their destination.

China is experiencing an accelerated aging process. Population aging brings not only the changes of the size and proportion of the elderly population but the corresponding changes of the other age groups，especially of the labor-age population group，which has more profound and direct impact on the society and economy. This study uses primarily the United Nations latest population forecasting results to analyze the challenges and possible impacts of aging on labor supplies of the labor market in China. This study shows that although aging would cause a decline in the working-age population，the occurrence of which would be slow before 2030; however，the young labor force would experience a rapid decline. In addition，the aging of the labor force itself，as well as the increasing degree of aging in rural areas call for extra attention，suggesting that it is necessary to prepare relevant policies in advance.

There have long been debates and conflicting arguments in the studies of population carrying
capacity． This paper examines dilemmas and challenges in the studies of population carrying capacity．There are three major difficulties in the research of population carrying capacity: difficulty in conducting quantitative models of population carrying capacity with empirical researches due to limitations in theoretical hypotheses，difficulty in accurately determining the results of population carrying capacity due to the changing nature and the complexity and uncertainty of the influencing factors of population carrying capacity，and difficulty in operationalizing policy measures deriving from the research on population carrying capacity．The author argues that population carrying capacity exists objectively，and scholars should not abandon their research just because of the difficulties and problems in the studies of population carrying capacity．There is a need in the research on population carrying capacity to disembarrass of that of biological carrying capacity．Studies on population carrying capacity need to be conducted in dynamic perspectives．

Since the reform and opening to the outside world there has been a rapid and continuing growth of non-agricultural transfer of rural labour force in China. The existing studies on this issue are largely confined to migration or regional transfer of rural labor force. Meantime, because of the limitations of available data, there are few studies with time-series analysis. In this article, following the definition of non-agricultural transfer of rural labour force, estimation is made of the amount and its time-series changes of non-agricultural transfer of rural labor force by using data derived from common primary statistics through simple calculations, with analysis of the dynamics of non-agricultural transfer of rural labor force in the context of China’s economic development and policy changes.