Background: The COVID-19 pandemic has brought unprecedented challenges to the world, creating significant impact on people's lives and subjective wellbeing. While previous studies have shown that students' wellbeing and how they manage their emotions are critical to students' learning, less research has considered their specific impacts on student engagement in online learning. Aims: The aim of this study is to examine how students' subjective wellbeing and emotion regulation strategies (viz cognitive reappraisal and expressive suppression) are associated with student engagement in online learning during the pandemic. Sample: A total of 965 students from a university in China participated in the study. Methods: The data were collected online during the COVID-19 from March to July 2020, which included measures of wellbeing, emotion regulation strategies, and online learning engagement. Results: Structural equation modelling results showed that wellbeing was positively associated with both the use of reappraisal and suppression. Moreover, mediation analysis showed that reappraisal partially mediated the relationship between wellbeing and all types of online learning engagement (including cognitive, emotional and behavioural engagements). Conversely, suppression was found to have a small mediating effect between wellbeing and behavioural engagement of online learning only. No such effect was found on cognitive and emotional engagements. Conclusions: The findings provide evidence on the positive relationship between wellbeing and both the strategies of suppression and reappraisal during the pandemic. However, only reappraisal has positive impact on learning, suggesting the importance of effective regulation strategies on students' online engagement. Theoretical and practical implications of the findings are discussed.