Combining the two-sided platform and complex networks theory，a diffusion model was proposed to describe the coupled dynamics of a third-party platform spreading on buyers’social network and sellers’competition network respectively． In the model，the probability of buyers adopting the new payment platform is the function of three variables，including platform service quality，the ratio of neighbors in their social network adopted the new payment platform，and the number of sellers who also adopted the new payment platform; likewise，the probability of sellers adopting the new payment platform is the function of three variables，including platform service quality，the ratio of neighbors in their competition network adopted the new payment platform，and the number of buyers who also adopted the new payment platform; the statistical mechanics method was applied to developing differential equation groups to describe the diffusion process of the new payment platform on buyers’social network and sellers’competition network respectively; the coupled diffusion dynamics on those two networks has jointly characterized the diffusion process of the new payment platform in buyers’and sellers’communities simultaneously． In order to elaborate the utilizing method and framework value，this paper discussed the estimation method of model’s parameters and the research ideas of extending the proposed model so as to investigate diffusion strategies．