The president under Taiwan's semi-presidentialism is not a ceremonial head of state. On the contrary, he or she has considerable powers and is the head of the political system. However, until now, there is rare study exploring the president's role on the process of law-making, making us know very little about his decision-making behavior. This study tries to explore the behaviors of President Chen Shui-bian on the process of law-making in 2000-2008, to improve the understanding of the role of the president beyond the words and design of the formal constitutional structure. The paper systematically explores the President's preferences of all important bills, and analyzes the mechanisms of the preference-making and the strength of his preference on each bill. Based upon these findings, we could realize more about the role of president under Taiwan's semi-presidentialism. And author wish it will supplement deficiencies of the existing literature.