Abstract Objective This study, based on the balance between risks and resources theory, aimed to explore the longitudinal actor and partner effects of work–family conflict on parental burnout and the moderating role of supportive coparenting. Background Parental burnout adversely impacts parents’ physical and mental health as well as their parenting behaviors. Therefore, exploring the risk factors of parental burnout and ways to buffer the adverse effects of risk factors has become an urgent issue. Method Using a longitudinal design, dyadic paired data were collected from 501 heterosexual parents of primary and secondary school students at two time points (6 months apart). Results The actor–partner interdependence model (APIM) results revealed that work‐to‐family conflict had a significant partner effect on maternal burnout, and significant actor and partner effects on paternal burnout; however, family‐to‐work conflict did not show significant actor and partner effects on either maternal or paternal burnout. Furthermore, the actor–partner interdependence moderation model (APIMoM) analysis indicated that perceived supportive coparenting could moderate the effects of work–family conflict on parental burnout, exhibiting both self‐matching and partner‐matching effects. Conclusion The results indicate work‐to‐family conflict within work–family conflict may be a critical risk factor for parental burnout. These findings also reveal the complexity of supportive coparenting in moderating parental mental health and parenting behaviors, indicating that coparenting can be a double‐edged sword in certain situations. Implications The findings of this study deepen the understanding of the mechanisms underlying parental burnout and offer insights for related family practices.