An important feature of mature markets is the diffusion between the competitive products． Network effect changes the traditional diffusion pattern，and has an important impact on individual choice behaviors． Previous studies focus on the rate and degree of diffusion at the level of aggregation，ignoring the social interactions and characteristics at the level of individuals． Based on the network effect，this paper discusses competitive product diffusion from the individual perspective． Firstly，a direct network effect function based on the social interactions is constructed，and an indirect network effect function is developed which reflects the cooperative effect of multiple complementary products． Secondly，individuals calculate their own profit at the current time and their expected profit at the next time． At last，they choose the right product for the next time according to decision-making mechanism of expected socialized benefit satisfaction． Simulations are used to study the diffusion system，and the result demonstrates that: the direct network effect and indirect network effect have distinct roles at different stages; the small world network is the optimum condition for competitive product diffusions; individual number distribution，personal preferences and individuals’judgment to the market have significant effects on diffusion．