To study the Internet public opinion evolution, an analysis method taking the parameters’ increment of the network and the Agent as the study object， which was based on social network analysis (SNA), was proposed. By the quantitative analyses of SNA properties, the general evolution rules of the incident in the Internet public opinion were revealed. The information for decision of guiding the public opinion was provided according to the rule. The method was verified with the records of an incident in Tianya BBS forum and the result showed that the study is practically useful.
