The blended course has shown its great potential to facilitate student learning. To understand students' psychological status and social interaction, this study explores flow level, social centrality, and academic achievement in a blended curriculum. Specifically, the study aims to investigate the fluctuation of students' flow over time, the participation and achievement of students at different flow levels, and the relationship among the three factors. Therefore, a 13-week experiment was conducted on a blended curriculum of computer science, in which a total of 35 freshmen were involved. The results show that students' overall flow level tends to be stable across the three stages in a semester. It is worth noting that the dimension of “challenges” has a significant change across three stages. Further, students with high flow levels have higher performance in the forum's social centrality and academic achievement than those with low flow levels. Nevertheless, the experiment did not offer enough evidence to confirm that flow has a significant moderating effect in the relationship between social centrality and achievement.