Simultaneous equation model is used in economic system model which often contains several interconnected and multivariate models. In this paper we selected the main factors that affected economic growth, and established a simultaneous equations model about population,the level of consumption and GDP. Through the actual economic data of Beijing from 2005 to 2011,we obtained the solution of the model and the results systematically described the interaction and influence between the factors of population,the level of consumption and economic growth in this region.