To investigate post-traumatic stress disorder (PTSD) in in-serviced nurses during COVID-19, and analyze the influencing factors. Methods: From May to June 2020, a self-designed general population data questionnaire and the PTSD Checklist–Civilian Version (PCL-C) were used to investigate 3762 nurses on duty during COVID-19, and make a comparative analysis of the difference between front-line and non-front-line nursing. Results: Among the 3762 nurses surveyed, the average PCL-C score was (42.18 ± 16.85), and the positivity rate of PTSD screening was 53.8%. Logistic regression analysis showed that the risk factors of PTSD included high administrative title, lack of post, fewer working years, low income, having children, and being non-front-line nurses. The control study showed that there were more front-line nurses in those who had higher incomes, worked more than two night shifts per month, worked in tertiary hospitals, and participated in disaster relief before. Conclusion: PTSD exists commonly in on-the-job nurses during COVID-19. Managers should pay full attention to those affected and take targeted and timely intervention measures.