Abstract: In P2P networks, the behaviors of popular file downloaded arc similar to the spread process of the epidemic diseases,which can be described by dynamics of infectious diseases spread. I}he diffusion process of P2P file was modeled in accordance with the epidemic dynamic model. And also the basic reproductive number was derived, which can determine the ability of file propagation. Further experiments are proved that the basic reproductive number obtained can describe the behavior of file propagation and reflect of the differential impact the different parameters on file diffusion fairly well.

Key words: P2P file sharing system, File diffusion, Propagation, Basic reproductive number, Influence factors