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．