The purpose of this paper is to explain the significance of the concept of sovereignty in politics. Before make discussion on the relations among sovereignty, political power, authority, and legitimacy, the framework will first consider the widely accepted definitions of sovereignty, sovereign, and states. It will then analyze the role of sovereignty in political theory by referring to the research circumstances of modern states and international relations nowadays. Finally, the following conclusions will be made that: (1) Conceptually, sovereignty is intimately associated with several fundamental political ideas such as power, authority, legitimacy and states. It even can be, to some extent, an extreme form of the complexity of them; (2) From a practical view, modern political society partly derives its security and stability from sovereignty, whether from the inside or outside.