Purpose The purpose of this study is to explore the Instructor’s adaptation process of school P.E. environment in middle school sports club and to develop substantive level theory. Methods For this purpose, 17 sports instructors who had worked for more than 3 years at the middle school in Seoul were selected as research participants. The method of this study is the Grounded theory(Strauss & Corbin, 1990). Results The results of this study are as follows. First, as a result of open coding, the instructor's adaptation process of the school P.E. environment was organized into 104 concepts, 30 sub-categories, and 15 categories. Second, as a result of axial coding, a paradigm model for the adaptation process of the school P.E. environment was formed. Third, as a result of the selective coding, created the storyline of the adaptation process and made the core category, ‘instructor's adaptation process of the school P.E. environment in middle school’. Four types of adaptation process such as 'Acceptance type', 'Effort type', 'Compromising type' and 'Abandoning type' are derived through the formalization applied to the hypothesis of the core category. Conclusions Based on these results, the developed substantive level theory was evaluated and summarized.