To explore the effects of family functioning on problem behaviour among Chinese preschool children, 1,025 preschool parents were assessed using the family assessment device, child problem behaviour scale, and parent-child relationship scale through a random sampling method. Based on the McMaster model of family functioning and the Process Person Context Time model, this study analysed the relationships between family functioning and children's problem behaviour, taking into account the mediating role of the mother-child relationship. The results showed that preschool problem behaviour was significantly positively correlated with mother-child conflict and significantly negatively correlated with mother-child intimacy. In particular, mother-child conflict played a mediating role between family functioning and problem behaviour in preschool children. The results of this study suggest that improving family functioning and reducing mother-child conflict play an important role in reducing the incidence of problem behaviour among Chinese preschool children and promoting their healthy development.