我國在政黨輪替後，主政者視台灣憲政體制為「向總統制傾斜的雙首長制」，而與歷任行政院院長之互動，便在主觀認為能夠強勢主導行政權，但實際過程卻迭受阻礙的落差間，造成閣揆角色大異其趣。本文將以我國憲法上行政權之設計與運作為中心，依據路徑依賴理論進行因果分析；透過路徑的幾個特定時序階段，包括：重大關鍵時刻與制度歷史起源、制度結構的變遷與所遭遇的危機，與行動者在其中表現的偏好與策略計算，經由實然與應然面次第觀察憲政體制中行政院院長與總統的互動關係，並評估其前景。基於歷史制度主義的精神，本文一方面關注時間脈絡，另一方面將時間當作行動序列的開展過程，除了強調制度結構對行動的束縛，亦提出行動改變制度結構的可能，期望依此而更能確認我國行政院院長之憲政定位，並進一步證明其正是憲政體制能否良性發展之關鍵。

Since the first party turnover occurred in Taiwan, the President has always regarded our constitutional system as a presidential system. However, even with a predominance of administrative power, the President has often met many great difficulties. Meanwhile, the five Presidents of the Executive Yuan (2000-2006) have acted as the staff who obey the instructions of the President, the leaders of the administrative branch, and even other roles. This paper is based on the design and operations of the administrative power granted by the constitution of Taiwan and is grounded in the theory of “Path Dependence,” and it performs cause-and-effect analysis according to historical context. Through several specific events, including crucial moments and, the origins of those moments, institutional changes and crises, and the preferences and tactics of various actors, we also plan to observe the starting point, development of this path, and assess its prospects. From a standpoint of historical institutionalism, this paper not only investigates the context of the history of the constitution, but also emphasizes the actions of relative actors in this history to discover that the institutional structure’s constraints are also the potential to change that structure. By highlighting the path dependence of the premier’s role after the party turnover in Taiwan, we conclude that the President of the Executive Yuan is the key person in advancing our constitutional system.