This case study uses qualitative data generated over three years to explore how a Chinese expert teacher constructs her personal practical theory (PPT) about teaching. The data analysis showed that the teacher successfully constructed a personally relevant, institutionally expected, and socio-culturally embedded PPT that manifested her teaching beliefs. The teacher constructed the PPT through five essential and interrelated steps: (a) identifying effective teaching practice; (b) crystalising a core concept from effective teaching; (c) proposing theoretical tenets around the core concept; (d) configuring the theoretical tenets into a preliminary PPT; (e) refining the PPT in relevant communities. The theory construction experience deepened the teacher's understanding of teaching and enhanced her confidence in engaging with educational theories and university-based scholars. However, the teacher's lack of knowledge about educational theories and hands-on tools for theory construction posed significant challenges to the teacher. This study generates new empirical evidence and conceptual insights into teacher theory construction, enriching international discussions on the theory-practice gap in education. The research findings also suggest practical implications for frontline teachers, facilitating their engagement with theories to close the theory-practice divide in their situated contexts.