Under the background of universal two-child and three-child policy, China’s fertility level continues to decline. The expansion of female birth spacing is one of important reasons for the decrease of fertility rate in China in recent years. Thus, it is the key to understand the low fertility rate in China in recent years to explore the influencing mechanism of birth spacing expansion. In this context, this study examines whether grandparents’ caregiving can significantly shorten the two-child birth interval, as well as the influence mechanism of paternal care on the birth interval of second child, which can find out the reasons for that hindering and delaying the birth of two children, so as to provide the basis for decision-making in the formulation of child-friendly policies. Based on the data of China Family Panel Studies ( CFPS ) in 2018, Cox regression model was used to verify the influence of grandparents’ care support on the birth interval between two children of women of childbearing age and its mechanism. Cox regression results show that grandparents’ care support can reduce the direct and indirect costs of women having a second child. Urban identity, education level and working hours played a positive regulatory role, in which grandparents’ care support has a greater influence on the birth interval among urban women, women with higher education level and longer working hours. This is because the direct economic cost of childbearing for urban women is higher; meanwhile the indirect cost of childbearing for women with higher education level is higher; moreover, women with longer work hours have higher work-family anfliots. Thus, grandparents’ care and support have greater influence on the decision of childbearing time of these women. It is suggested that full recognition should be given to the procreation promotion role of grandparents’ caring support in the family and financial subsidies should be provided for families with two children. Optimizing the market for care services, providing more public childcare services and extending maternity and parental leave to meet family care needs should be recommended. Meanwhile it is recommended to reduce female employment discrimination and maternal punishment to support women to have two and more children.
