To describe the social network in online forum （BBS）of university, social network analysis and data mining method was used to investigate the network relationship of community under the help of UCINET software and ID3 algorithm. Characteristic of community network, formation of opinion leader’s position and the relationship between initiative and other attributes of community members were also explored. On this basis, we proposed some advice in order to solve key problems of the community, for example how to get more better communication in the university online forum, how to make the students are more positive, how to make students learn more knowledge here.