Objective To investigate mental health of the middle-aged and elderly population during the outbreak of coronavirus disease 2019(COVID-19)and the influencing factors. Methods A questionnaire survey was conducted online of the mental health of the middle-aged and elderly people aged 50-65 years in China. The survey included self-rating questionnaire-20 (SRQ-20), patient health questionnaire-9 (PHQ-9), generalized anxiety disease-7(GAD-7) and insomnia severity index (ISI), which were used to eva-luate stress response, depression, anxiety, and sleep disorders. SPSS statistics 20.0 was used for statistical analysis. Multiple linear regression analysis was employed for the impact of influencing factors on the mental health. Results Of collected questionnaires,1501 (nSRQ-20=1377, nPHQ-9=1241, nGAD-7=1204, nISI=1209) were effective. Among the respondents, 24.5% had psychological stress, 18.5% moderate or severe depression, 10.7% moderate or severe anxiety, and 10.8% moderate or severe insomnia. Multiple linear regression analysis showed that physical health, worry about the epidemic, education level and age had a greater impact on the mental health. The determination coefficients R² of the four factors in PHQ-9, GAD-7, SRQ-20 and ISI models were 0.190,0.176,0.232 and 0.137, respectively, of which the physical health was the most significant, and the standardized β values were 0.374,0.368,0.406, and 0.322, respectively (P<0.01). Further analysis of the difference of mental status with different health conditions (good, general and poor) showed significant differences among the three groups in the four dimensions of stress response, depression, anxiety and sleep disorders (P<0.001). Conclusion The middle-aged and elderly population, particularly the unhealthy people, suffer more mental problems during the COVID-19 outbreak.