WeChat has become an indispensable part of university students' life in China. However, there was little research into the relationship between WeChat and learning. This study investigates university students' attitudes towards the impact of WeChat on learning, the determinants of WeChat learning engagement, and how WeChat usage influences students' academic performance. A total of 719 valid questionnaires were sent and collected from university students. The results indicate: (1) WeChat is perceived as a "double-edged sword" of learning with two-sided effects; (2) students' engagement with WeChat on learning is at the upper-medium level, over which the motivation of WeChat usage, other than usage duration and login time, is found to have strong explanatory power; and (3) the frequency of WeChat usage affects students' academic performance in a complicated way with self-control playing a moderating role. The findings have significant value for future research about WeChat usage among university students.