Teacher Professional Learning Community (PLC) has been proved an effective way to promote teacher knowledge, enhance teaching practice, and achieve better student learning outcomes. However, various levels of contradictions exist during sustaining and developing the PLC which impede the teacher's professional development. Using activity theory as theoretical schemata and activity systems analysis as a method, this paper explored the contradictions in the joint activity of a college English as a Foreign Language (EFL) teacher PLC in the form of action research. Three levels of contradictions were identified. The primary contradiction is one between the different value systems of the subjects, the secondary contradiction being one between the tool and outcome in the central action research activity system, and the third contradiction being one between the central activity system and the adjacent activity of teachers' daily teaching practice. The data indicated that the resolution of the contradictions via expansive learning could contribute to the development of the PLC. The findings may provide implications for the effective in-service teacher education of college EFL teachers.