With the development of wireless network technology and the surge of mobile internet users, the self-media internet public opinion(SMIPO) with the new media platform of WeChat, micro-blog and etc. has gradually replaced the traditional media public opinion, it has become a dominant force in the field of public opinion and has an important impact on social stability. Based on this background, this paper firstly defines the concept of SMIPO's forwarding network, discusses the forwarding effect of forwarding network, and analyzes the main impact factors of forwarding effect in SMIPO. Then this paper constructs the SMIPO diffusion model based on the forwarding effect, and simulats the public opinion diffusion model. Simulation results show that the super group, which is the central and important node of the rapid spread of SMIPO in the forwarding network, causes the obvious dynamic cascade characteristics of public opinion in the media network. In addition, the SMIPO diffusion has the divergent characteristics in the stage of appearance, amplification and stability, and diffuses and disseminates in the form of merging effects, super groups and centralized topology.