The Bass's innovative diffusion model, which takes the time factor into consideration, is improved and applied to the diffusion problem of Internet purchasing population. The factors impacting the number of Internet purchase are analyzed. Based on the data of Internet population from 1981 to 1998, comes out the following conclusions: First, the influence of changing p-the impact of mass media on the potential Internet purchaser is greater than that of changing q-the impact of oral promulgation on the potential Internet purchaser. Second, while and q both remain unchanged, the initial Internet purchasing population N(1) has little impact on the development of Internet purchasing population N(t).