Objective: To investigate the characteristics of post traumatic stress disorder (PTSD) in college students during the outbreak of COVID-19, and to explore the mediating role of psychological resilience between social support and PTSD. Methods: By using direct selection method, 572 college students in Anhui and Shanghai were selected and administered with General Characteristics Questionnaire, the PTSD Checklist Civilian Version(PCL-C), Psychological Resilience Scale(PRS) and Social Support Rating Scale(SSRS). Results: Among the participants, 25.0% had moderate PTSD symptoms, 11.7% had obvious PTSD symptoms, and the positive rate of PTSD was 36.7%. The prevalence of PTSD in college students was higher in males than in females ( χ 2= 4.31， P <0.05). The junior students were higher than other students ( χ 2=16.81， P <0.01). The scores of social support, psychological resilience and PTSD were (33.79±4.83), (92.17±13.39) and (35.50±11.39), respectively. The correlations of all variables were statistically significant( r =-0.49-0.76， P <0.05); The mediation test showed that social support could not only negatively predict PTSD directly(direct effect was -0.35), but also indirectly affect PTSD through psychological resilience(indirect effect was -0.32). Conclusion More than one third of college students have PTSD symptoms, and psychological resilience plays a partial mediating role in the relationship between social support and PTSD,social support can both directly and negatively predict PTSD and indirectly affect PTSD by increasing an individual s psychological resilience.