This study mainly aims to explore the spatio-temporal patterns and to simulate the future scenario of population change in Beijing based on the fifth and sixth census data at township level. The main contents and results were summed up as follows: (1) The resident population of Beijing increased with an average annual rate of 3.5% between 2000 and 2010, and the population increased by 0.6 million every year. Beijing was one of the megacities which were classified into the first range for their great amount of increased population. (2) There was an obvious circle structure in space. The population of inner city was almost stagnant; it had a rapid growth in the suburbs, and a high rate in the outer city. However, it had an increase only in the county seat and the key towns in the ecological conservation region of Beijing. (3) In terms of the CA/MAS scenario simulation analysis, in the spontaneous layout scenario, employment opportunities will be further agglomerated to the inner city, while population is suburbanized constantly. This will increase the city's commuter stress and aggravate the condition of city traffic block. When adjusting the parameters of employment and thus strengthening the guide policy of urban population living in working function, the problem of imbalance between industrial space and residential space in the urban internal space scale can be solved. At the same time, the formation of cluster of small towns can be promoted and urban commuter pressure can be reduced. Then comes the city’s radiation and diffusion effect. The authors suggest that, in order to optimize the spatial distribution of population in Beijing, more efforts should be made to coordinate the relationship between employment and residents. An important way is to accelerate regional coordinated development, and to plan multi-centers development as groups.