The present study focuses on the relationships between principal support, school-wide inclusive practices, teacher agency, and teachers' professional skills in the Chinese context of inclusive education -- Learning in Regular Classroom. Data were collected from 1,676 primary and junior high school teachers in China. Results of structural equation modelling demonstrated that principal support had a significant effect on teachers' professional skills; the chain mediating role of school-wide inclusive practices and teacher agency on the relationship between principal support and teachers' professional skills was also significant. These results suggest the direct and indirect roles of school principal in promoting inclusive education teachers' professional skills. The results also highlight the significant effects of school environment on inclusive education teachers' professional development. We consider implications for practice at the end of the paper.