The purpose of this study is to find the differences of introvert-extrovert trait on the degree of flow and participation mode at the on-line discussion. The data for this research was collected from the total of 40 learners. The research data is testified through ‘MANOVA method’. The results of this study were summarized as followed : Firstly, the learner's introvert-extrovert trait affects the learner's discussion flow degree. That is, the introvert trait was more effective than the extrovert trait in the discussion flow degree. Secondly, the learner's introvert-extrovert trait affects the learner's discussion positive participation degree. That is, the introvert trait was more effective than the extrovert trait in the discussion positive participation degree. lastly, the learner's introvert-extrovert trait affects the learner's discussion negative participation degree. That is, the extrovert trait was more effective than the introvert trait in the discussion negative participation degree. Based on these research results, it was suggested that introvert-extrovert trait should be utilized in order to improve the discussion flow and participation on the on-line discussion.