Background: The outbreak of the COVID-19 pandemic has caused extensive public health concern and posed great challenges to the medical services, including the mental health concern for psychiatric patients who were one of neglected groups. The current study aimed to assess the prevalence and risk factors of post-traumatic stress disorder (PTSD) symptoms among psychiatric patients in China during the pandemic. Method: Self-reported questionnaires were distributed to psychiatric patients in several psychiatric hospitals in Beijing China from 28 April to 30 May 2020. The socio-demographic information and psychiatric symptoms such as PTSD, anxiety and depressive symptoms were collected by using The Impact of Event Scale- Revised (IES-R), the 7-item Generalized Anxiety Disorder Scale (GAD-7) and the 9-item Patient Health Questionnaire depression scale (PHQ-9). Multivariate regression was used to analysis the related factors for PTSD symptoms. Results: 1,055 psychiatric patients were included in the final sample. The prevalence of PTSD symptoms was 41.3%. Risk factors for PTSD symptoms and its subscales included old age, high risk perception, symptoms of anxiety, symptoms of depression. Conclusions: The prevalence of PTSD symptoms is high among psychiatric patients during the COVID-19 pandemic in China. We call for more concern and PTSD interventions to relieve the psychological stress of psychiatric patients during the pandemic.