中文摘要：

随着单独二胎政策的放开，计划生育政策再次引起了人们的关注．为评估生育胎次对中国人口数量的影响，本文建立了关于人口增长的动力学模型．首先，分别对辽宁省和新疆自治区的人口数据进行了拟合，评估了“二胎”政策对两地区人口的影响．其次，对全国人口数据和抚养比进行了拟合和预测．最后，通过参数敏感性分析，评估各因素对总人口增长的影响．

英文摘要：

With adjustment of ＂two-child policy＂ that a couple can have a second child, provided that one party of them is the only children, the family planning policy aroused more attention once again. To assess the impact of the number of births on China＇s population, this paper establish a dynamic model about population growth. First of all, this paper applies this model to fit the population data of Liaoning province and Siukiang autonomous region and evaluate the influence of ＂two-child＂ policy on the population of the two regions. Secondly, this model is applied to fit and forecast the population data and the dependency ratio of China. Finally, sensitivity analysis is carried to assess the effect of various factors on population growth