There is growing evidence that the COVID-19 pandemic has had an impact on the mental health and professional identity of nursing students. This study aimed to explore the trajectories of psychological dis-tress and professional identity and examine their causal relationship among graduate nursing students. A prospective longitudinal study was conducted with 556 graduate nursing students in China who were asked to complete the Questionnaires for Emergent Events of Public Health and the Profes-sional Identity Questionnaire for Nursing Students at three timepoints dur-ing the pandemic (T1 = onset of the outbreak, T2 = state-wide isolation, T3 = school reopening). The results showed that psychological distress and psychological identity changed over time, with the lowest psychologi-cal distress and highest professional identity at T3. The cross-lagged analy-sis showed that professional identity at T1 and T2 negatively predicted psychological distress at T2 and T3. We concluded that nurse educators should develop programs and strategies to cultivate professional identity in graduate nursing education to improve mental health during public health crises.