Non-suicidal self-injury (NSSI) is being increasingly recognized as a prominent mental health concern, especially among adolescents. In psychiatric clinical samples, its incidence is high and difficult to identify. However, few studies have explored the NSSI behavior of psychiatric hospitalized adolescents. This study aimed to explore the influencing factors of NSSI according to the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) in adolescents admitted to the psychiatric department. In this cross-sectional study, by convenient sampling, a total of 505 psychiatric adolescent inpatients aged 10-19 years completed questionnaires to record details of sociodemographic characteristics, the NSSI questionnaire, the Child Psychological Abuse and Neglect Scale (CPANS), the self-report version of the Strengths and Difficulties Questionnaire (self-report SDQ), the Coping Style Scale for Middle School Students (CSSMSS), which were compared between NSSI inpatients and non-NSSI inpatients. This study used the diagnostic criteria for NSSI disorder in DSM-5: adolescent patients who have NSSI behaviors for more than 5 times in the past 1 year are called NSSI. A multiple logistic regression model was built to explore the relationships among general information, CPANS, SDQ, CSSMSS, and NSSI. Risk for NSSI is quantified by odds ratio (OR) with 95% confidence interval (CI). The results showed that 77.82% (n=393) of adolescent inpatients had NSSI, and 80.0% were female (n=404). NSSI adolescent inpatients experienced more family scolding, psychological abuse, and neglect and showed more positive attitudes toward NSSI than non-NSSI adolescent inpatients. However, after controlling for covariables, the difference disappeared. NSSI behavior was significantly associated with female (OR =2.391, 95% CI: 1.396-4.097, P=0.002), younger age (10-14 years old) (OR =1.876, 95% CI: 1.154-3.049, P=0.011), have close friends (OR =0.355, 95% CI: 0.164-0.768, P=0.008), peer discussion about self-injury (OR =1.977, 95% CI: 1.047-3.734, P=0.036), emotional and behavioral difficulties (OR =1.853, 95% CI: 1.054-3.258, P=0.032), problem-oriented coping styles (OR =0.968, 95% CI: 0.945-0.991, P=0.007), emotion-oriented coping styles (OR =1.035, 95% CI: 1.006-41.064, P=0.016). Measures should be taken to prevent and reduce the occurrence of NSSI behaviors among hospitalized adolescents in psychiatric department, which include improving adolescents' attitude towards NSSI, reducing adolescents' gathering behavior in the ward, preventing adolescents from discussing NSSI through social media, improving their coping style when facing difficulties, and reasonably regulating their abnormal emotions and behaviors.