Infant  mortality  has  an  important  place  in  mortality  research ，which  is  the  beginning  of  the mortality  force changes by age and which also affects later － life mortality change． Analysis of the past censu- ses demonstrates that a large gap exists between the census － reported infant mortality rate and the actual rate as a result of underreporting． By analyzing the relation between infant mortality and economic development of 174  countries of the world，comparing census data with health statistics ，and examining provincial variations in infant mortality ，it is found  that  there  is  significant  underreporting  in  infant  mortality  in  the 6th  census． Since  errors in the reported mortality of the population aged 1 － 4 are relatively small ，we first adjust it by areas ，then adjust infant mortality according to the steady relation between infant mortality and mortality of the population aged 1 － 4． The  adjusted  national  infant  mortality  rate  stood  at 17． 27‰  in 2000 ，implying  that underreporting rate of the infant mortality in the 6th census is about 78% ．

In the past,almost all the accuracy evaluations of China’s population census data represented a high quality and there was no specific age mantissa orientation.However,the survival-rate analysis of the two censuses shows the existence of systematic errors of demographic data and the age mantissa orientation.In this paper,the author presents a new method to test the accuracy of the population age data,and uses this method to analyze China’s census data to find out that the age mantissa orientation of demographic data does exist.The author also finds that the age mantissa orientation and the error differ from each other in the five times of population censuses.Finally,the author tells us that the first and fifth population census has a better data-accuracy than other censuses.

Suburbanization is one of the stages of urban development.Some scholars suggest that the big cities in China have generally entered the stage of suburbanization.This paper examines in details the city of Beijing which is described earliest by the scholars to be typical of suburbanization.Since the 1980s,concentration has mainly characterized migration in Beijing.Change in population distribution is a result of adjusting population in central urban districts.Urban development is represented by geographical expansion of the central urban districts.This suggests that urban development in Beijing is in the stage of urbanization rather than suburbanization.Characteristics in population change in different stages of urban development from urbanization to suburbanization are discussed,and the author argues that the big cities in China,with the exception of Shanghai,are still in the stage of urbanization.