<p>This cross-sectional study explored how childhood trauma affect mobile phone addiction (MPA) in adolescents with depression through alexithymia and coping styles. 2268 adolescent participants aging from 12 to 18 who were diagnosed with depression were recruited in China. A moderated mediation model was constructed to examine the role of alexithymia and coping styles in the relationship between childhood trauma and MPA. 2239 patients completed the questionnaires in the study. Childhood trauma was found to be positively related to alexithymia and MPA. Alexithymia was positively related to MPA, and played a partial mediating role in the relationship between childhood trauma and MPA. In addition, problem-focused coping had a negative effect on alexithymia, and there was a positive relationship between childhood trauma and alexithymia when problem-focused coping at the high level. Adolescents who experienced childhood trauma tend to have high probability of MPA. Alexithymia and problem-focused coping styles played a mediating role in the relationship between childhood trauma and MPA. This provided treatment guidance of MPA by avoiding traumatic experiences when childhood and encouraging adolescents to adopt problem-focused coping style to solve problems.</p>