The problem of online rumors has been a hot and difficult point in academic research, especially after the occurrence of public emergencies. Clarifying the triggering mechanism of online rumors in public emergencies is the basis for reducing rumors. Based on the three dimensions of information source, information channel and information audience in information dissemination theory, 7 antecedent conditions are extracted by qualitative comparative analysis method. The truth table composed of 40 selected cases is imported into fs/QCA3.0 software to form conditional configuration relationship. It is found that interest demands become the necessary factor for triggering online rumors, and the configuration paths of "information channel-information audience" consensus lack and "information source-information audience" resonance effect constitute the main triggering scenes of online rumors. The differences between government and media in playing roles and presenting methods are the internal inducements for triggering online rumors.Therefore, the governance of online rumors should expand the expression channels of netizens' wishes and simplify the network appeal link; Grasp the realistic scene triggered by online rumors and pay attention to differentiated coping logic; Clarify the role orientation of the government and the media, and realize the benign interaction between them.