Background and objectives: Childhood maltreatment is strongly associated with major depressive disorder (MDD) in adulthood, social support may mediate the effect of childhood maltreatment on MDD, but there were few studies exploring the mediating role of different types of social support between childhood maltreatment and MDD, and whether sex difference existing in the mediating models was also unclear. Methods: The study included 965 MDD patients and 443 healthy participants from nine centers in China. MDD patients are diagnosed using the DSM-IV. The Childhood Trauma Questionnaire-Short Form, Social Support Rate Scale, and 17-item Hamilton Depression Rating Scale, were used to assess the status of childhood maltreatment, social support and MDD, respectively. Multivariable mediation analyses were used to examine the mediating role of different types of social support between childhood maltreatment and MDD after controlling for sex, age, ethnicity, educational level, family history, work status and marriage. Results: The childhood maltreatment increased the risk of MDD. All types of social support significantly reduced the risk of MDD. Total social support (β = -0.37, 95%CI: -0.43, -0.30, p <0.001), perceived support (β = 0.05, 95%CI: 0.03, 0.07) and support utilization (β = 0.01, 95%CI: 0.01, 0.12) played a mediating role in childhood maltreatment and MDD, respectively,but not tangible support. For males, only perceived support mediated the relationship between childhood maltreatment and MDD, while for females, both perceived support and support utilization mediated the relationship.