This study investigates a longitudinal cross-lagged relationship between social support and resilience among parents of autistic children within the framework of conservation of resources theory. It also examines the mediating role of active coping and conducts a group comparison between preschool-aged and school-aged children within this relationship. In total, 436 parents of autistic children aged three to fifteen years from China participated in this study. They completed the Social Support Questionnaire, the Connor-Davidson Resilience Scale, and the Coping Strategies Inventory at baseline (Time 1 [T1]) and 6 months later (Time 2 [T2]). A longitudinal cross-lagged structural equation modeling approach was applied. The findings indicated a longitudinal bidirectional relationship between social support and resilience over time, with active coping mediating this interaction. While the overall model did not significantly differ between parents of preschool- and school-aged children, the relationship between resilience at T1 and social support at T2 was significant for the school-aged group. The study highlights that social support and resilience mutually reinforce each other and that active coping serves as a key mechanism underlying this relationship. Considering the variation across age groups, this study offers implications for age-specific family services aimed at enhancing resilience and social support for parents of autistic children.