Exploring Mutual Learning of Four Chinese Senior High School EFL Teachers in a Collaborative Action Research Community

English as a Foreign Language (EFL) teachers' professional development has been attached much importance with the advent of the National English Curriculum Standards (NECS in short) for Senior High Schools as it initiates the shift from knowledge-skill-oriented education to competence-oriented education. As an effective way for teachers' professional development, collaborative action research community is introduced in this study to provide teachers with opportunities for mutual engagement, meaning negotiation, and a shared repertoire. Four senior high school EFL teachers from four different schools were studied in a collaborative action research community to explore how teachers from diversified backgrounds achieve mutual learning for their professional development. With data collected from observation, interviews, and journals, the study reveals that diversity and partiality help maintain mutual engagement in the community of practice. Meaning negotiation and mutual accountability in a joint enterprise contribute to the coherence of the community. Moreover, the participative activity of online and offline group discussion and the common topic of thinking visualization were treated as sources of a shared repertoire, an essential indication of a harmonious community. In this case, this study extrapolates how the collaborative action research community achieves harmony to support teachers' professional development in action research.