With its rise, China has increased its soft power while U.S.'s has declined. China's growing use of soft power in Southeast Asia presented new challenges to U.S. foreign policy. By downplaying many conflicting interests and working collaboratively with countries and regional organizations on such issues as territorial disputes and trade, Beijing has largely allayed Southeast Asian concerns that China poses a military or economic threat. With the decline of America's soft power, China's diplomatic engagement has earned the country greater respect in the region. China has not only enhanced its relations with Southeast Asian states, but has also diminished U.S. power and influence in the region. This research adopts the ”soft power” approach to analyze the construction and competition for soft power in Southeast Asia between U.S. and China. This essay first defines soft power as the basis of analysis. In order to understand the construction of the soft power in Southeast Asia, a further dissection of U.S. and China foreign policies respectively is needed. Finally, the paper analyzes the implications of soft power competition between the two countries, and suggests U.S. and China future policy options in this region.