<p>This study examined the mediating role of childhood maltreatment between family structure and adolescent depressive symptoms, utilizing a nationally representative sample of Chinese adolescents (<i>N</i> = 30,234). Depressive symptoms and childhood maltreatment were assessed with the Patient Health Questionnaire (PHQ-9) and the Childhood Trauma Questionnaire (CTQ), respectively. Compared to adolescents in two-parent biological families, those in single-parent, grandparent-headed, and other families exhibited a significantly higher risk of depression. Conversely, multigenerational families demonstrated a protective effect. Emotional abuse (OR = 4.565, 95% CI: 4.118–5.061), physical abuse (OR = 1.774, 95% CI: 1.584–1.986), sexual abuse (OR = 1.884, 95% CI: 1.637–2.169), emotional neglect (OR = 1.658, 95% CI: 1.540–1.785), and physical neglect (OR = 1.301, 95% CI: 1.211–1.397) were all identified as significant risk factors for adolescent depression. Mediation analysis revealed that childhood maltreatment significantly partially mediated the link between family structure and depression, explaining 21.32% of the risk in single-parent families, 8.46% in grandparent-headed families, and 9.40% in other families. These family structures are associated with elevated risks of adolescent depression, partially through the pathway of increased childhood maltreatment. These findings underscore the necessity for targeted interventions that address family-based adversity to improve mental health outcomes in vulnerable adolescent populations.</p>