To research the formation law of network public opinion, from the angle of theory of Complex Adaptive System (CAS) and started from the constitution of public opinion, this article introduced the concept of Incline Degree of Opinion of Agent for the first time, and analyzed the related factors influencing the changes of incline degree of opinion of agent and set up the rules for the changes. The authors then established a model with the influence of Agent, debating efficiency, self-supporting capability, active flag and the influences of mainstream media and law as the independent variables to explain the formation of network public opinion. Finally simulation experiments were carried out after simplifying this model and the experiment results were analyzed.
