Based on an analysis of the decisionmaking process of the American government in arms sale to Taiwan since the establishment of diplomatic relations between China and the United States, the article employs the rational behavior model, the transagency politics model and the bureaucratic politics model to explore US policy of arms sale to Taiwan. The author holds that each of the three models only partially explains US policy but none of them alone would give a complete explanation. Only by combining the three and taking into consideration of all factors influencing foreign policy decisionmaking can we make a relatively comprehensive appraisal of US policy of arms sale to Taiwan.