Objective: This study was performed to explore the effect of childhood trauma on nonsuicidal self-injury (NSSI) in adolescents with bipolar II (BD II) depression. Methods:Based on the diagnostic criteria of the DSM-5 and structured interviews to assess the presence or absence of NSSI, 184 adolescent patients with BD II depression were divided into the NSSI (n = 112) and non-NSSI (n = 72) groups. The Adolescent Nonsuicidal Self-Injury Assessment Questionnaire (ANSAQ), Childhood Trauma Questionnaire-Short Form (CTQ-SF), Toronto Alexithymia Scale (TAS-20), Hamilton Depression Scale (HAMD), and Hamilton Anxiety Scale (HAMA) were used to assess the subjects. Result:The CTQ-SF, HAMD, HAMA, and TAS-20 scores were significantly higher in the NSSI group than in the non-NSSI group (p < .01). Logistic regression analysis showed emotional abuse (p = .028, OR = 1.14, 95% CI = 1.01-1.28) and age of onset (p = .009) as risk factors for NSSI. Adolescents with onset age 12-13 years (OR = 6.30, 95% CI = 1.72-23.10) and 14-15 years (OR = 2.24, 95% CI = 1.04-4.84) had a higher risk of self-injury relative to adolescents aged 16-18 years. Conclusion:Childhood trauma and alexithymia were important influencing factors in adolescent patients with BD II depression. Emotional abuse and age of onset as risk factors for NSSI, and difficulties in emotion recognition were positively associated with the patients' NSSI.