In the information society, the spread of online public opinions on natural disasters has gradually become a new problem concerned by people. We analyzed the influencing factors of information dissemination, the characteristics of natural disaster information dissemination and the index elements of natural disaster grade evaluation. Then, a series of indicators and factors were selected, and combined with the characteristics of natural disasters, the influencing factors of natural disaster information dissemination were summarized and analyzed. After that, the system dynamics model of natural disaster information transmission was established. The basic data were determined by means of questionnaire survey and expert scoring, and the information transmission process of natural disasters was studied from the perspective of dynamic simulation. We believe that the information dissemination of natural disasters has an obvious life cycle, the duration of which is generally 15-20 days, and different levels of disasters have little impact on the information dissemination cycle.