PIP: A good fertility model can accurately explain a population's fertility process. It is widely acknowledged that the general decline of fertility in China over the past two decades is closely associated with the popularization of contraceptive knowledge and methods. The use of various contraceptive methods has a clear and definite impact upon both the fertility level and the fertility model. Commonly used fertility models fail to adequately explain how to measure that impact and how to introduce contraception factors into fertility models to simulate China's fertility process in order to provide relatively objective information on family planning practices and the creation of population policies. A birth duration fertility model with contraception factors is established on the basis of China's fertility process. The model may be used in studying the influence of simulated contraception factors upon the fertility level and the fertility model, and in making predictions about the number of births.