Maternal depression risk is a worldwide health challenge, and family support is an important factor affecting maternal depression risk, however, its role and contribution in the fluctuation of maternal depression before and after delivery is rarely studied. Based on the survey data, combined with regression and decomposition analysis methods, the contribution degree of family support factors to the fluctuation of maternal depression before and after delivery was analyzed. The results showed that :(1) family support significantly affected the risk of maternal depression; (2) After childbirth, the risk of depression decreased significantly, and the combined contribution of family support factors and medical factors accounted for 50%; (3) The total contribution of family support factors is larger (about 30%) than that of medical factors (about 20%), and the main factors include care status, medical care level and parents-in-law relationship. The findings are helpful to deepen the understanding of the relationship between family support and maternal depression, and attention to the construction of family support system should be an important part of the development strategy of women's health throughout the life cycle.