The aim of this study was to assess the feature change of nonsuicidal self-injury (NSSI) behaviors in bipolar disorder before and during the pandemic. A total of 115 adolescents with NSSI were evaluated using a Wechsler Intelligence Scale for Children–Fourth Edition, Kiddie Schedule for Affective Disorders and Schizophrenia for School-Aged Children–Present and Lifetime Version, and some related scales. In comparison with the 2017 group, female sex, borderline personality disorder, self-reported internalizing disorders, anxiety/depression, and thinking disorders were all related with the 2021 and 2019 groups. The 2019 group was linked to a variety of somatic issues. Negative life experiences, bullying, eating disorders, social issues, depressed feelings, performance and social anxiety, and rejection sentiments were all linked to NSSI. Both shared and differential features between before and during the pandemic may represent possible change for diagnostic and preventative interventions of NSSI in patients with bipolar disorder. Therefore, the doctor should adjust the treatment strategy based on changing of features between before and during the pandemic.