The relationship between peer support and academic engagement has been widely explored. However, scarce research examined this relationship for college students, and little was known about the underlying mechanism under this relationship. This study aimed to examine the effect of peer support on academic via the mediation of academic motivation and the moderator of academic anxiety. This model was examined among 4581 Chinese college students (mean age = 20.22, SD = 0.92) who completed the measurement of peer support, academic motivation, academic engagement and academic anxiety. The results revealed that for Chinese college students, peer support significantly positively predicted academic engagement (r = 0.755, p < 0.001) and academic motivation could mediate the relationship between peer support and academic engagement ([beta] = 0.036, 95% CI [0.493, 0.638]). Moreover, as a moderator, academic anxiety weakened the correlation between peer support and academic motivation ([beta] = -0.048 95% CI [-0.062, -0.033]). The current research highlights the mechanisms underlying the relationship between peer support and academic engagement, which played a vital role in facilitating college students' academic engagement.