Contract theory is a democratic theory about society and politics. In the history of social and political thought in the west for thousands of years, there are various contract theories. Their views or theories are not consistent, but they are generally related to the democratic trend of social development. Contract theorists use the concept of contract to explain social and political phenomena, and their concept of "contract" is based on the so-called concept of "equality". Most contract theorists believe that an independent, equal and harmonious life is a natural life that conforms to human nature. Therefore, the relationship between people should be equal consultation, voluntary and mutually beneficial. Only through equal consultation can we link our wishes with those of others.