Abstract: Risk society has changed the evaluation criterion of major projects and the agenda setting of decision-making. Major projects are becoming risk sources to social instability, which have triggered many mass incidents. Social stability risks of major projects are related to the social expectation of stakeholders, which includes three forms: benefit expectation, security expectation and legitimacy expectation. All of them lead to social instability behavior or behavioral tendencies directly. Encompassing the social expectation into the framework of social risk assessment, the social effects can be observed objectively and comprehensively, and then the social conflicts can be prevented effectively.