Informed by an ethnographic approach, this study aims to investigate the professional culture of a group of English as a foreign language (EFL) teachers in a high school in China. Relying on data gathered through extended field observation and in-depth interviews, this study seeks to uncover the distinctive characteristics of EFL teacher culture as well as its underlying influencing factors. The research findings show that the participants formed a positive work culture which evolved in tensions. Professionally, the participants' aspirations and commitments toward teaching were in tension with limited resources; institutionally, a democratic relationship was in tension with an authoritative leadership; emotionally, the teachers' emotional wellbeing was in tension with contextual constraints. The participants' co-constructed culture played a positive role in promoting their collaborative learning and continuing development, which in turn contributed to their teacher culture.