In the present era of network information communication, the network public opinion, which has received a wide range of attention, is being generated rapidly when significant events occur. As a result, it has put a great deal of pressure on all departments, institutions, and individuals in the society, which cannot be ignored. Previous studies on dam failure risk and social impact simply considered the measurable impacts of important facilities, cultural relics, and so on, ignoring their effect on “people”. The main subject of the project is the impact of dam failure risk on the dam engineering community that consists of government, water administrative department, reservoir management organization, as well as the affected downstream public and media. In this paper, research on the social impact’s formation mechanism of dam failure risk is clearly demonstrated, and its diffusion hierarchy of dam failure risk is elaborated. The nine roles classified under dam break risk, namely direct encounters, responsible people, handlers, supervisors, related encounters, disseminators, sympathizers, followers, and avoiders, are analyzed. The social impact’s evaluation indicators of dam failure risk are also studied, namely personnel loss, publicity, news, and duration. Taking Dahe Reservoir as an example, practical application shows that the assessment results are highly reliable, objective, and reasonable, and have classification accuracy. This assessment method provides a platform for the comparative analysis of the social impact of different dam failure events based on grade evaluation and easy operability. The data obtained is more objective and easily collected, which proves the validity of the assessment results.