The current study assessed 869 elementary school students in China using self-report questionnaires, to examine the multiple mediating effects of academic self-efficacy and positive academic emotions (enjoyment and relief) in the relations between teacher support and academic engagement (cognitive, behavioural and emotional aspects) within a math class. The results indicated that teacher support exerted a direct and significant impact on the three aspects of math engagement. Both academic self-efficacy and enjoyment mediated the relations between teacher support and the three aspects of math engagement, whereas relief did not mediate such relations. Moreover, teacher support affected math engagement through multiple paths from academic self-efficacy to both enjoyment and relief. Relief displayed a smaller effect on the three aspects of math engagement than enjoyment did. However, we did not find substantial difference in the underlying mechanisms of different aspects of engagement. Limitations and educational implications were also discussed.