Abstract: Purpose/Significance Eliminating the irrational behavior of the public plays an important role in overcoming the impact of public health emergencies. Design/Methodology Taking the COVID-19 epidemic as the research situation, this paper constructs a theoretical model of the generating mechanism of public irrational behavior in public health emergencies based on the Stimulus-Organism-Response model, which is summarized from the news and online reviews on social platforms by Grounded Theory. Accordingly, this paper carries out systematic interpretation for the model. Findings/Conclusions The model shows that the generation of public irrational behavior follows four key processes: emergency situational stimulation, irrational behavior decision-making, irrational behavior implementation, and irrational behavior regulation. Information sources and information dissemination channels will affect the information processing quality of the public, which is moderated by event response. Public irrational behavior decision-making is a complex process. The information processing quality of the public affects their psychological perception directly, which is regulated by psychological distance. The public’s risk perception, responsibility perception and gains-losses perception bring about an irrational emotional reaction, which is the premise of the public’s irrational behavior. However, due to the differences in personality, knowledge and previous experience, the fluctuation of the public’s emotions is quite different. Irrational behavior may be directly led by irrational emotion or implemented after behavior evaluation. The former mainly produces emotion-focused behaviors, while the latter mainly produces problem-focused and interest-focused behaviors. Irrational behavior regulation will help to adjust the public’s irrational emotions, reduce the occurrence of irrational behavior, and accelerate to overcome the COVID-19 epidemic in an all-round way.