Major powers and their roles in international relations are always important studying subjects and interesting research topics for students of international relations. Definitions for major power have been discussed. It is argued that at present major powers can be classified into three kinds, namely supper power (1), major powers (10) and middle/or regional powers (30), and the rest (140) cannot or will not become power due to their lack of both necessary soft and hard strength. The international order in the last 500 years has constantly changed thus reflecting the changing power status. Therefore, after the disappearance of the two-polared world the international order will be a multi-polared, not uni-polared one, the authors argued. People all over the world are striving to build a democratic and just world order in which every country, big or small, will have a roughly equal saying in issues affecting international peace and security.