The parent-child relationship plays an important role in shaping adolescents' mental health during the COVID-19 pandemic. However, the mechanisms underlying the association between the parent-child relationship and mental health are unclear. Using a 2-wave longitudinal design, this study examined the role of both mother-child and father-child relationships during home quarantine in boarding school students' internalizing and externalizing problems after school reopening, and the mediating roles of academic buoyancy and academic engagement. A total of 1967 boarding high school students completed a battery of self-report questionnaires before and after school reopening. Results indicated that both father-child and mother-child relationships indirectly contributed to internalizing and externalizing problems through the interlinked mediation path of academic buoyancy and academic engagement. The mother-child relationship had greater influence on internalizing and externalizing problems than the father-child relationship. These findings clarify the associations between the parent-child relationships and mental health problems of boarding high school students during the transition to school reopening in the COVID-19 pandemic, expanding our understanding of psychological adjustment related to parent-child relationships and the potential mechanisms of these relationships.