This study adopted a framework based on social cognitive theory to explore the influence of thinking styles on critical thinking and multiple mediation effects of student assessors' assessment performance (scoring and review comments) between them. Samples were 97 graduate students enrolled in the "Seminar" course at a university. Students used an online assessment system and the evaluation form to conduct peer assessments for peers' reports. Findings revealed: (1) thinking styles primarily had an indirect effect on critical thinking solely through comment performance (complete mediation effect), and it indirectly influenced critical thinking serially through scoring performance and comment performance (completely serial mediation effect), but it cannot solely influence critical thinking through scoring performance. (2) thinking styles directly influenced both scoring and comment performance, and also indirectly affected comment performance through scoring performance (partial mediation effect). (3) scoring performance indirectly influenced critical thinking through comment performance (complete mediation effect), while comment performance directly influenced critical thinking. (4) scoring performance directly influenced comment performance. The main contribution of this study lies in proposing and validating a multiple mediation model of "Thinking Style-Online Assessment Performance-Critical Thinking", indicating that student assessors' online assessment performance (scoring and comment performance) has multiple mediation effects between thinking styles and critical thinking. This result holds significant academic and practical implications.