American’s military presence in Syria may be divided into three stages namely from sending troops to the garrison（2015-2017），planning deployed and expanded（2017-2021），long-term military presence in Syria（2022-）. Currently，the United States，Russian，Iran and Turkey，these countries have military presence in Syria，despite there is some difference about Kurdish forces between the United States and Turkey. The objectives of the military presence of the United States are fivefold，namely combating against the ISIS，having control of the oil resources and the wheat productions，supporting the opposition force even the extreme force，maintaining the balance and even advantages of the Russian and keeping the deterrence to the Syria government. As to the influences，the military presence of the United States has have invasion of the sovereignty of Syria. While disturbing the situation of the northwestern region of Syria，the military presence of US has been a negative factor of US-Turkish relation. Additionally，the security of the US base also has been threatened by ISIS and other forces. In the future，the United States will maintain the military presence and enforce them in order to counter Russian，Iran and the Syria government. However，it’s must be pointed out that American’s military presence in Syria is illegal and a barrier to the solution of the Syria crisis and the reconstruction of Syria.