Science and technology museums should serve as pilots in emergency science popularization while facing unexpected public events. However, after the outbreak of COVID-19, the offline science popularization was hindered by the epidemic of novel coronavirus pneumonia, so it is of great significance that science and technology museums turn to online emergency science popularization. Current research proposed an online emergency science popularization solution based on contextual model of science communication to respond to the epidemic. Taking the characteristics of public knowledge absence under emergency context into consideration, the emergency science popularization routine for science and technology museums has been designed in three steps, namely the demand triggering step, the emergent communicating step and the feed-back-evaluating step. What’s more, the experiences of online emergency science popularization practiced by China Science and Technology Museum in the course of combating COVID-19 are summarized, and suggestions are put forward.