Over the past one century and more, in response to the domestic and international factors such as the protection of small producers, consumer welfare, international competitiveness, and world war, influenced by the dominant political and economic ideologies such as Harvard School and Chicago School, the goals of antitrust policy in the United States varied greatly in different periods. No matter active or reactive, the antitrust policy for mergers and acquisitions has always played a role of "carrot and stick", and profoundly affected the market structure, corporate behavior and industrial development in the United States. Judging from the actual policy effect, neither the "carrot" or "stick" policy has been able to effectively prevent the general trend of mergers and acquisitions of American companies. Benefiting from the improvement of the US government's antitrust index, the license for cooperation in production, R&D, marketing, and procurement, and the antitrust exemption in specific areas since the 1970s and 1980s, mergers and acquisitions for economies of scale and technological innovation have been easier than before. These policies have also affected and shaped the direction of the US semiconductor, aircraft manufacturing and the Microsoft’s case accused of monopoly. Under the background of global industrial concentration and fierce competition, it is worth learning the experience and lessons from the US antitrust policy, particularly for those late-developed countries which aim to cultivate the local large enterprises through mergers and acquisitions while regulate them effectively.