In President Obama’s last year in the White House，there is little change on the overall pattern of American diplomacy，either from the perspective of geopolitics or over the major issues concerned. The Obama Administration spent more energy on domestic issues in the election year. With the coming end of the 8 years in the White House，the top priorities of President Obama were influenced by his intention of leaving diplomatic legacy to some extent. The Obama Administration concentrated on the main issues such as the rebalance strategy，non-proliferation，anti-terrorism，the US-Russian relations，the US-Cuba relations，etc. However，with Donald Trump winning the election unexpectedly，the power transfer brought more uncertainties on American foreign policy. This article also analyzes the general trends of the Trump Administration’s foreign policy and the difficulties it will face in the future. As the article points out，the implementation of the Trump Administration’s foreign policy will be influenced greatly by internal and external environment，especially the decline of American power and its ability to dominate the world.