During the COVID-19 pandemic, nursing professionals have faced increasing mental health challenges. Despite this, there is a lack of research examining post-traumatic stress disorder (PTSD) specifically among nurses in Medical Alliances. This study sought to explore factors contributing to PTSD in nurses working within the Regional Medical Alliance (MA) in Shantou, China, during the early stages of the pandemic. From February to March 2020, 1,286 nurses across four MA hospitals participated in the study. The findings showed that 15.6% of nurses experienced PTSD, while rates of depression, anxiety, and sleep disturbances were 35.5%, 18.3%, and 36.4%, respectively. PTSD was found to be significantly associated with higher levels of depression, anxiety, and sleep problems. Further analysis using logistic regression revealed that nurses working in tertiary hospitals, older nurses, and those with more severe depression, anxiety, or sleep disorders were at greater risk for developing PTSD. These results underscore the need for targeted mental health support for nurses at higher risk within Medical Alliances.