Objective To explore the impact of the participation of patients with chronic mental illness in health promotion activities on their physical, psychological, and social functions. Methods This study included inpatient with chronic mental illness from a hospital in Eastern Taiwan. According to the experimental research design, the selected subjects were randomly divided into a health promotion group and a control group, with 60 people in each group. The health promotion team conducts health promotion activities twice a week, each for approximately 50 minutes, over the course of eight weeks (16 times in total). The measurement instrument adopts the Adult Mental Health Scale (AMHS) scale. Five experts and scholars in related fields are invited to conduct expert validity. Results Using independent sample t-tests to analyze the changes in the two groups after 8 weeks, the physical, psychological and social problems of the health promotion group were significantly improved compared with the control group. Conclusion Health promotion activities can alleviate the physical illness, anxiety, irritability, depression, and social distress of chronic hospitalized mental patients, and can also increase their positive and optimistic mood. It can provide chronic mental health care institutions to plan patients’ physical activities or exercises.