In the social media era，the process of the spread of risk information has undergone tremendous changes，and the impact of social media use on public risk perception has become increasingly strong.In this study，the “Shandong Vaccine” incident，which was shocked by the country in 2016，was taken as an example，and the social network analysis method was used to carry out a comprehensive and accurate quantitative analysis of the various relationships in the social network.The final results show that the risk information dissemination network in the event is based on the dynamic network structure of the authoritative sources and the key actors，the source has the important information source，the key actors in the risk information diffusion process as the opinion leader，makes the risk information in the dissemination amplified，can be faster to spread to ordinary actors.