Abstract Background The off-label use of antipsychotic medications is common in many countries, and the extent of such use in psychiatric inpatients in China has not been sufficiently studied. The purpose of this study was to survey the incidence and examine the correlates of off-label antipsychotic use in a large, nationally–representative sample in China. Methods This study included discharged psychiatric patients between March 19 and 31, 2019 from 41 tertiary psychiatric hospitals across 29 provinces in China. Their socio-demographic and clinical data were collected and analyzed. Results After excluding patients with schizophrenia spectrum disorder or bipolar disorder, 981 patients were included in the analysis. Overall, antipsychotics were prescribed to 63.2% (95%CI 60.2–66.2%) of the sample. Antipsychotics were used in a wide spectrum of psychiatric disorders, with the rate being the highest among patients with dissociative (conversion) disorders (89.9, 95%CI 83.0–94.8%), organic mental disorders (81.7, 95%CI 73.1–88.7%), dementia (79.0,95%CI 67.8–87.9%), obsessive-compulsive disorder (77.8, 95%CI 55.7–92.5%), mental disorders due to psychoactive substances (75.3,95%CI 64.7–84.2%), behavioural and emotional disorders with onset usually occurring in childhood and adolescence (71.4, 95%CI 45.5–90.1%), somatoform disorders (63.2, 95%CI 40.8%–82..2%), major depression disorder (53.7,95%CI 48.8–58.6%), anxiety disorder (38.8,95%CI 30.5–47.7%), and insomnia (25.0, 95%CI 8.5–28.9%). The top three most commonly used antipsychotics were olanzapine (29.1%), quetiapine (20.3%) and risperidone (6.8%), and their corresponding average doses were 9.04 ± 5.80 mg/day, 185.13 ± 174.72 mg/day, and 2.98 ± 1.71 mg/day, respectively. A binary logistic regression showed that younger age, having the Employee Health Insurance or Residents Health Insurance, having psychotic symptoms and requiring restraint during hospitalization were significantly associated with off-label use of antipsychotics. Conclusion Off-label use of antipsychotics is very common in psychiatric inpatients in China, mainly with moderate-dose use of single agents. However, the efficacy and safety of this practice is uncertain for many diagnoses and for the elderly. Clinicians should be cautious about this practice while waiting for more research data.