Background: Since the outbreak of COVID-19, online courses have been extensively used from K-12 to higher education. Online learning engagement, an important factor in online learning success, is currently at a low level in high school. Meanwhile, the research on the factors that influence high school students' online learning engagement is still limited. Objectives: Based on the theories of regulatory focus and value control, this study developed a multi-mediation model to investigate whether self-efficacy and academic emotions can mediate the relationship between regulatory focus and online learning engagement. Methods: A total of 926 high school student (52.16% female, mean age = 16.47 years) were recruited to participate in this study and completed self-report measures of regulatory focus, online learning engagement, online learning self-efficacy and academic emotions. And we used SPSS macro PROCESS developed by Hayes to examine the mediating role of online learning self-efficacy and academic emotions. Results and Conclusions: The results indicated that promotion focus had a stable positive effect on online learning engagement of high school students, whereas prevention focus had a significant negative effect on the same. Self-efficacy and positive emotions had a significant positive mediating effect between promotion focus and online learning engagement. Moreover, positive emotions had a significant positive mediating effect between the prevention focus and online learning engagement, while negative emotions had a significant negative mediating effect between them.