In the context of the increasingly integrated development of information technology and classroom instruction, university students are engaging in a growing portion of their learning within online spaces. Against this backdrop, the investment in online learning engagement has become a topic of significant interest among numerous researchers. Prior studies have indicated that social presence is a crucial predictor of online learning engagement, However, the underlying psychological mechanisms are unclear. To bridge this research gap, we surveyed 722 Chinese university students (280 males and 442 females, mean age = 18.88 years, SD = 1.13), all of whom completed a self-report questionnaire. Drawing the social presence theory, this study employed Mplus 8.3 to develop and examine a multiple mediation model incorporating social presence, interpersonal interaction, flow experience, online learning engagement. The results revealed that: (1) social presence, interpersonal interaction, and flow experience were significantly and positively correlated with online learning engagement; (2) social presence can directly predict college students' online learning engagement, as well as indirectly influence their online learning engagement through three indirect paths: the independent mediation of interpersonal interaction, flow experience and the chain mediation of interpersonal interaction and flow experience. This study sheds light on the psychological mechanisms by which social presence promotes online learning engagement among college students, providing insights for addressing the "screen dilemma" in online learning.