In order to find out the influence of Korean Middle School Students' relationship by science class applying STAD cooperative learning, this study conducted a social network analysis and sought to analyze the communication networks within the group and identified the change process of the type. The subject of this study was 30 students of the second grade at the girls' middle school located in Korea's Metropolitan City. For five weeks, science class applying STAD Cooperative Learning was implemented in the 'reproduction and generation' chapter. First, the class social network analysis showed that all the prices of density, degree centrality, closeness centrality, and betweenness centrality have risen after science class applying STAD Cooperative Learning. Also, the classroom's relationship index has improved. In other words, STAD Cooperative Learning encouraged interaction among students. Second, in order to research popularity, students' centrality analysis through the class social network analysis showed that top-ranked students' values of density, degree centrality, closeness centrality, and betweenness centrality appeared commonly high after science class applying STAD Cooperative Learning. Third, the analysis of the communication network change within six groups showed that all channel type appeared most often and circle type also appeared anew after science class applying STAD Cooperative Learning. In other words, it was possible to exchange information freely and communicate with all members of the group through STAD Cooperative Learning.