This study explored changes in preservice teachers' beliefs about teaching in early childhood education during teaching practicums in China. Data from four preservice teachers' beliefs were collected through interviews and reflection journals. Based on Bronfenbrenner's theory, an ecological system framework was used to explore the change factors. The findings indicated two change orientations: elaboration and integration. Elaboration incorporated situated reflection, positive emotions, and interactions with children and mentors to explain belief change. Consistency between practices and beliefs with positive emotions and strong agency reinforced their beliefs. Integration of beliefs can be ascribed to teaching dilemmas that arouse negative emotions, parental expectations, and the field school's culture, which weaken agency and social culture in the ecological framework's nested system. Therefore, belief change can be attributed to individual factors that interact with the ecological system. The study elucidates how changes occur in preservice teachers' beliefs. Teacher education programmes should address the constraints and enabling factors during teaching practicum.