This paper analyzed the documents regarding how principals improve the quality of curriculum, teaching and learning. Based on the principals’ responses, this study utilized the categories of direct impact and indirect impact to analyze the behaviors and roles of 22 secondary school principals’ reactions. The major findings of this paper included that principals used policy making, high expectation, modeling, and direct guidance to exercise their direct influence on teaching and learning. Second, principals utilized the mechanisms of structure, human resource, micro-politics, and culture to provide their indirect impact on teaching and learning. Third, principals used more indirect impact on improving quality of curriculum, teaching and learning. Fourth, some principals used only indirect impact to improve quality of curriculum, teaching and learning. Finally, this paper provided suggestions related to improving the quality of the practice of leadership development for principals.