This study aims to investigate how principal's leadership is related to school performance in terms of multi-level indicators such as school's organizational characteristics, teachers' group-level and individual-level performances, and students' performances. In the study, strong leadership represents that a principal can be supportive and foster participation for teachers, can develop clear goals and policies and hold people accountable for results, can be persuasive at building alliances and solving conflicts, can be inspirational and charismatic, and can encourage professional development and teaching improvement. The strong leadership is found associated with high organizational effectiveness, strong organizational culture, positive principal-teachers relationship, more participation in decision, high teacher esprit and professionalism, less teacher disengagement and hindrance, more teacher job satisfaction and commitment, and more positive student performance particularly on attitudes to their schools and learning. The findings support that principal's leadership is a critical factor for school performance at multi-levels. Implications are advanced for further study and development of leadership.