This thesis explores the role the U.S. plays in the developmental process of international nonproliferation regime. The argument of this thesis is mainly based on the power-based perspective, which assumes that the U.S., the first country to obtain nuclear technology, profoundly influences the creation and persistence of the nonproliferation regime. First of all, I discuss the debate on the theories of international regime in order to highlight the applicability of power-based approach in the research of nonproliferation regime. Secondly, I examine both the nuclear policy of the U.S. and the developmental history of nonproliferation regime, so as to explain the former¡¦s impacts over the latter. Finally, I evaluate the different means and postures of the U.S. when she confronts different violators. Through this inquiry, I attempt to expose the flaw of the nonproliferation regime: the proliferation problem is still not totally suspended even after the establishment of the nonproliferation regime. The main factor of the flaw is, nonetheless, resulted from the U.S.¡¦ misapplication of her nuclear hegemonic power and her selective proliferation policy towards different violators, although she had positively contributed to the creation and persistence of the nonproliferation regime.