Previous studies have illustrated a robust relationship between academic self-efficacy and academic performance. However, the underlying psychological mechanism of this relationship is still unclear. This study employed a moderated mediation model to examine whether academic buoyancy (ability to deal with academic challenges and setbacks in school daily life) mediated the relationship between academic self-efficacy and academic performance and whether social support moderated the mediation process. A total of 860 (M = 16.39, SD = 0.73) high school students in China completed questionnaires on academic self-efficacy, academic buoyancy, and social support. Academic performance was measured by standardized tests. The results indicated that academic buoyancy partially mediated the association between academic self-efficacy and academic performance. Social support moderated the first half of the path of the mediation model. The findings of the present study provide educational guidelines and suggestions for improving academic performance among high school students.