To determine the prevalence of overweight and obesity in patients with severe mental disorders (SMD) and the factors associated with their socio-demographic and disease characteristics in a cross-sectional population-based study. This analysis examined the prevalence of overweight and obesity in 14 868 managed SMD patients in an urban area of Shenzhen city based on data from the health information monitoring system in 2021. Multivariate logistic regression were used to identify the factors associated with the prevalence of overweight and obesity in patients with SMD. China. 14 868 patients with SMD. The prevalence of overweight and obesity in patients with SMD in this study was 32·6 % and 16·1 %, respectively. In multivariate analysis, married status, Shenzhen household registration, management durations of 5-10 years and >10 years, participation in family physician services, taking clozapine or aripiprazole, FPG > 6·1 mmol/l, hypertension, TC ≥ 5·2 mmol/l, TG ≥ 1·7 mmol/l, and more frequent follow-ups in the past year were associated with higher odds of overweight and obesity. Compared to their respective reference categories, living with parents, spouse and children, taking risperidone, aripiprazole, amisulpride and perphenazine, FPG > 6·1 mmol/l, hypertension, TC ≥ 5·2 mmol/l, TG ≥ 1·7 mmol/l, and more frequent follow-ups in the past year were associated with higher odds of obesity. We observed a high prevalence of overweight and obesity in patients with SMD in this study. The findings highlight the need for integrated management of overweight and obesity risk factors among patients with SMD.