The Grand Strategy, which aims to protect the country’s security as well as its national interest, is a reflection of the nation’s ability to mobilize its national resources in order to fit its supreme goal in a long period of time. In the early stage of post-Cold War era, the U.S. government had soon formulated a Grand Strategy which aimed to maintain its ″primacy″ worldwide as well as to construct and dominate a liberal international order. This Grand Strategy was formulated upon ″five pillars″: defending homeland security, maintaining the balance of power, punishing ″rogue states″，establishing democratic peace and assisting allies overseas. Hence, the Grand Strategy, both by its means and ends, has been generalized as a trending topic among politicians and academics. In the short term, adherence to a Grand Strategy of ″primacy″ will help the United States to keep its global interests and reach its strategic goals. In the long run, the reliance of existing Grand Strategy has created a kind of ″path dependence″ effect, which finally evolves to strategic inertia. As a result, it is difficult for political elites to adjust the existing Grand Strategy as well as to improve it. In order to make a further understanding of the strategic inertia inside the U.S. Grand Strategy, this paper starts to analysis the U.S. government’s organizational inertia. Three factors that gradually generated and enhanced the strategic inertia are: (1) the commitment to compliance, (2) the solidification of cognition, and (3) the bounded rationality. With the help of U.S. official publications, declassified archives, media news and think tank reports, this paper tries to finger out the causes of the strategic inertia within the U.S. government, and then find its influence on the U.S. Grand Strategy. This paper believes that the strategic inertia of the United States was formed and deepened during the period of the Bush (the 41st President) and Clinton administrations. During the Bush (the 43rd President) administration, there had been many critics pointing out the negative effects of the strategic inertia posed on the Grand Strategy. However, the government generally ignored these alerts. At the beginning of his first term, Obama realized that this kind of inertia had already become a constrain of the further strategy development. However, limited reform had been taken and it was difficult to change the status quo. By the time that Donald Trump came into power, ″overcoming inertia″ had already become one of his primary political tasks. Although the Trump’s reform has encountered many obstacles, the strategic inertia has not yet stagnated and still move on gradually. This paper is the first research attempt to use the theory of strategic inertia to discuss the evolution of U.S. Grand Strategy in the post-Cold War era. Based on the comparative analysis between U.S. governmental documents and the country’s actual behavior, our work verifies the hypothesis that the post-Cold War Grand Strategy of the United States has been restricted by the strategic inertia. For this reason, the development and implementation of the U.S. Grand Strategy has been constrained. This means that any effort to adjust this strategy from the decision-making community will be restricted by this strategic inertia. It is still a myth whether or not Trump administration could keep trying to overcome the strategic inertia in the future.