Although 2007 is already the fifth year of the U.S. invasion in Iraq，the U.S. troops are still in the predicament of Iraqi religious faction and terrorist attack.To get out of this dilemma，Bush and his aides worked out a new military reinforcement strategy toward Iraq at the beginning of this year，which has been the most important foreign policy undertaking for Bush administration as well as a hot point of international relations in 2007.In September 2007，Bush announced that the new strategy has brought an initial positive effect and the U.S. troops will be partially withdrawn from Iraq soon. In the short or mid term，the U.S. would have great difficulties to improve Iraqi security situation profoundly no matter withdrawing or reinforcing its military capabilities. In the long term US politicians would rather keep its military presence in Iraq based on the U.S. national interests in terms of its global strategy，its Middle East policy，and Iraq as a democracy exemplar and especially as an oil base.