BackgroundDuring the COVID-19 outbreak, most Chinese college students were home-quarantined to prevent the spread of the virus. COVID-19-associated impact has been shown to be a risk factor for the development of post-traumatic symptoms disorder (PTSD). However, little is known about the psychological processes that mediate this association. This study investigated the association between COVID-19-associated impact and PTSD and examined whether past stressful events, psychological resilience, and social support have mediating effects on this association.MethodsThe 12,397 valid responses from 31cities in China via an online survey assessed PTSD symptoms, past stressful events, psychological resilience, social support and social-demographic variables. AMOS was used to test the hypotheses of mediating effects.ResultsOn the 39th day of the declared COVID-19 epidemic in China, 6.75% of the surveyed sample showed PTSD symptoms. A positive mediating effect of past stressful events was found between COVID-19-associated impact and PTSD, whereas psychological resilience and social support had negative mediating effects. The fit indices for the path model were found to be significant (β = 0.28,p< 0.001), COVID-19-associated impact indirectly affects the risk of PTSD through mediating pathways (past stressful events → psychological resilience → social support) on PTSD.ConclusionsAttention should be paid to the effects of past stressful events of Chinese college students who were home-quarantined during the COVID-19 epidemic, and strategies should also be implemented to improve social support and develop psychological resilience.Trial registrationThe study was approved by the ethics committee of the Southwest Minzu University.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12888-023-04906-6.