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， this study analyzed the contribution degree of family support factors to the fluctuation of maternal depression before and after delivery. The results showed that family support significantly affected the risk of maternal depression. The risk of depression decreased significantly after delivery. The combined contribution of family support factors and medical factors accounted for 50%. The contribution of family support factors is larger （about 30%） than that of medical factors （about 20%）. The main factors include care status， medical care level and parents?in?law relationship. Family support plays critical role in preventing maternal depression， and the construction of family support system should be an important part of the development strategy of women’s health throughout the life cycle.