The development of a city cannot be separated from people, and the occurrence of city emergencies has a great psychological impact on the city public. The city public, while generating great psychological panic, has doubts on the governance ability of the government, which is extremely unfavorable to the development of a city. In order to avoid the formation of group psychology under city emergencies, based on the rheology-mutation theory, this paper analyzes the development law of group psychology under city emergencies and puts forward effective measures to avoid the formation of group psychology. The results show that the formation of group psychology follows the law of change to sudden change after city emergency, and the government can effectively reduce the formation of group psychology and avoid the occurrence of secondary social security events by timely and effective emergency rescue and avoid rumors and gossip spread.