In this paper, we study the adjustments of birth control policy on population. By using the national census data during 1985 to 1995, we establish a grey prediction model to forecast the total population in the future 15 year and compared it with the actual data. The conclusion is drawn that the birth control policy controls our country's population growth rate to some extent. Then, based on grey-relevant method, we analyze the factors affecting population growth in 2000 to 2010, and we obtain that the age structure and sex ratio are two main influencing factors. Based on these two main factors, we conclude that the family planning policy had an impact on population structure in our country, especially accelerated the ageing problem and the sex ratio imbalance.