In the "top-down" reform of the teacher personnel system, the principal is the core of policy implementation, who also serves as the secretary of the Party organization. We focus on which type of leadership should principals choose to maximize his impact on teachers' professional ability and work stress. The HLM method was used to conduct a longitudinal study of teachers in Mentougou District of Beijing from 2013 to 2015. 603 teachers from 34 schools participated in this research. It is found that the policy couldn't affect teachers directly, the principals plays a role as a bridge between them. Taking the role of secretary, the principal's transformational leadership behavior can "accelerate" the development of teachers' professional ability and "filter" stress; but the transactional leadership behavior of the principal as an administrative role failed; transformational leadership has a greater impact on schools with higher SES. Principals needs to transform into transformational leadership especially in rural areas.