Abstract: This article attempts to interpret teaching autonomy in view of teacher knowledge and to explore the correlation of the dual factors. The authors, on the basis of a case study, conduct a thorough analysis of the case teachers’ knowledge bases by means of interviews and class observations. The article then draws the conclusion that the case teachers’ descriptive knowledge is correlated with their observational one and that their knowledge bases form their teaching autonomy. It is argued that EFL teachers’ knowledge base has crucial effect on and then forms their teaching autonomy.