The objective of this paper was to explore the impact of social support on the academic achievement of master's students and the mediating effect of academic emotions in the impact mechanism. This paper collected data from 567 master's students at J University and analyzed it using SPSS 26.0 and Amos 23.0. The results showed that social support significantly predicted academic achievement. Specifically, all three dimensions of social support (family support, supervisor support and institutional resource support) significantly predicted academic achievement. Positive academic emotions mediated the relationship between social support and academic achievement, with the indirect effect, while negative academic emotions had no significant effect on academic achievement. Therefore, to promote academic achievement of master's students, universities should create a supportive university environment and optimize the mode of postgraduate training and management, and constantly improve the support of supervisors. Additionally, master's students should cultivate the self-regulation abilities to better stimulate positive academic emotions among them.