Major changes have been made on American foreign strategy after President Obama took office. Combined“hard power”with“soft power”，“smart power”becomes a concept guiding American foreign strategy. The Obama administration forsakes the unilateral policy of the Bush administration and emphasizes international cooperation，dialogue and negotiation. The readjustment is typically reflected by the US policy on arms control，the shift eastward of the focus of anti-terrorism，the “return to Asia” policy，and the reset of the US-Russian relations. However，the readjustment of American external strategy doesn’t change the essence of its foreign policy. And such readjustments are constrained by multiple factors，including domestic political and economic situation and the development of international situation. The changes of American foreign strategy have brought both favorable and unfavorable implications for China.