The establishment of equator principles is a landmark in the financial market and even in the history of financial development. As their extensive application in the market of project finance, equator principles have gradually become the industrial standard and international conventions of project finance. However, compared with traditional legislations, equator principles are norms of self-regulation without the involvement of national forces, and their general principles and legitimacy source definitely break a new path. The evolution of equator principles experienced three phases: emergence, popularity and internalization, and the attribute of advocates of regulations, during which the nature of regulations and the character of financial industry played key roles. Meanwhile, factors such as “power,” mutual benefits, co-determination, effectiveness and even internalization of regulations by international financial companies, constitute the “legitimacy” source of equator principles. Besides, pointing at the defect of “norms of self-regulation,” advocates and practitioners endeavor to improve the “legitimacy” of equator principles.