[Purpose/significance] Based on the SOR(Stimulus-Organism-Response) model, this study explored the ef? fect of social support on user engagement based on the mediating role of emotion in online health communities.[Meth? od/process] Taking social support as the "Stimulus" (S) factor and emotion as the " Organism "(O) factor, this paper studied the mechanism of users' " Response" (R).We obtained 465 337 posts by 244 users from an online health com? munity as sample data. The hierarchical regression analysis is used to test the conceptual model. [Result/conclusion] The results show that information support, emotional support and social support provided by the online health communi? ty had a positive impact on the users' engagement behavior. In addition, user emotion has a significant partial mediating effect on the relationship between social support and user engagement behavior, and this mediating effect is moderated by user gender, that is, the mediating effect of emotion has a greater impact on male users.