This article explores whether a learning community can affect students' learning achievement and engagement. Besides, this study also analyzed whether degree centralities of peer interaction affect learning achievement and learning engagement based on social network analysis. While the experimental group combined the English learning system with the online learning community, the control group was simply using the English learning system. The results indicated that the students' engagement from the online learning community were higher than the ones who used the English learning system only, although the learning achievement is not significant difference between these two groups. Moreover, higher interaction learners from the online learning community revealed better performance in learning achievement and student engagement. Other than that, the learners who played the "Center" emerged with a higher learning achievement as well as the students' engagement than the "Periphery" ones. The research provides suggestions for online learning with learning communications as well.