During the Obama Administration，US-ROK Alliance experienced further development. With the deadlock of North Korea nuclear issue，US-ROK Alliance moves toward the direction of institutionalization. Aiming to cope with issues beyond ROK-DPRK crisis，US-ROK Alliance is becoming an important part of the US Asia-Pacific rebalance strategy. The fourth nuclear test by DPRK in 2016 undoubtedly reinforced the US-ROK Alliance. But the disputes and contradictions between the US and ROK remain in various fields. With the development of politics and economy both in the US and ROK，the alliance still faces uncertainties in the future.