Taking the approach of narrative inquiry, this study detected an excellent high school EFL teacher’s teaching stories and examined the development of her practical knowledge with the lens of activity theory. This study found that the development of the teacher’s practical knowledge is a process of expansive learning driven by internal contradictions, full of various contradictions and tensions. The reflexive practice based on contradictions and the teacher’s strong agentive intention of development are the major factors toward the development of teacher practical knowledge, but the teacher’s love towards students is the source of teacher practical knowledge development. This study indicates that teacher education needs to touch teachers’ own experiences and the essential issues of teaching environments.