Objective: To study the chain mediating effect of perfectionism and stress on cognitive avoidance and rumination. Methods: A total of 5412 college students were surveyed by Cognitive Avoidance Scale, Perfectionism Scale, Stress Scale and Rumination Scale. Results :(1) correlation analysis showed that there were significant positive correlations among cognitive avoidance, perfectionism, stress and rumination (r = 0.324-0.484, P < 0.001); (2) Cognitive avoidance had a significant positive effect on rumination (t = 0.347, P < 0.001), (3)perfectionism partially mediated the relationship between cognitive avoidance and rumination([0.1096,0.1429], P < 0.001), pressure partially mediated the relationship between cognitive avoidance and rumination ([0.0584, 0.0878], P < 0.001) , perfectionism and stress played a significant role in the chain mediation between cognitive avoidance and rumination ([0.0034,0.0070], P < 0.001) . Conclusion: Cognitive avoidance can directly affect rumination and indirectly affect rumination through the chain mediating effect of perfectionism and stress. This study reveals the relationship between cognitive avoidance and rumination and its mechanism.