Through case study，content analysis and questionnaire，this study explores the communication features and the psychological mechanism of the rumors published on official accounts of WeChat during the period from April 2015 to March 2016，discovering that when being exposed to rumors，the majority of people tends to hold a “rather believe it to be true” attitude，which decreases their critical thinking competence and makes them more susceptible to rumors. Based on the new features of online platform such as WeChat，this study proposes a formula regarding the influence of rumors，i.e. The influence of rumors =（the importance of an event x the uncertainty of this event）÷（the perception of control of the public x the critical thinking competence of the public）.