In order to protect the interests of trade in China, America paid much attention to the united market and the stability inside. America didn't want to see the situation that China would be separated by other mighty nations or pocketed profit without sharing with anyone else. At the same time, America considered that the political situation in China had to be kept steady, or other mighty nations would find opportunities to intervene. But America didn't care whatever governmental forms China might adopt. However, when the Hung-syan Imperialism caused a series of civil wars and Japan supported the powers of anti Yuan Shih-kai in the dark or toppled Yuan Shih-kai in public, America didn't take any actions. First, this article will analyze the reasons why America supported Yuan Shih-kai. Second, what influence did America bring in the process of imperialism. Last, why did America watch the failure of Yuan Shih-kai and his imperialism with folded arms? What factors did America consider in the process of making policies.