The public's risk perception of public health emergencies will determine their behavior choices to a certain extent. Research on public risk perception of emergencies is an integral part of crisis management. From the perspective of the whole life cycle, this article takes the COVID-19 epidemic as an example. It conducts empirical analysis to study the influencing factors of public risk perception of public health emergencies. The results show that: (1) the public's risk perception is affected by individual factors, event characteristics, social influencing factors, and individual relationship factors. (2) The more the public is familiar with the epidemic, the lower the risk of the epidemic. The more the public can control the loss of the epidemic risk, the perceived epidemic risk will be reduced. The more the public trusts the supreme power of the government, the lower the risk of the epidemic in their hearts is. The higher the closeness of the risk and impact of the epidemic to individuals, the higher the level of risk perception is. (3)The public's risk perception will evolve with the development of the situation, and there are differences in recognition of government departments' control measures at different stages of public health emergencies. The relevant departments should effectively guide the public's risk response behavior in combination with the life cycle of public health emergencies. The research conclusions of this article clarify the dynamic evolution of risk perception and provide a specific reference for the emergency management of public health emergencies.