The present invention relates to a computer simulation system of public security emergency management and a simulation method. A public security emergency management cloud platform is upwards connected with an emergency command platform, is downwards connected with the town and street emergency command systems, is transversely connected with the municipal special emergency command platforms on the basis of integrating the data resources and the communication network resources of the conventional various systems, thereby realizing the monitoring, the prediction, the early warning, the auxiliary decision-making and the command and dispatch, and providing the comprehensive information services for the emergency rescue and command, the accident deduction, the emergency disposal training and the emergency hedge skill training. The public security emergency management cloud platform comprises an emergency command hall, a basic supporting system, a comprehensive information service system and a mobile emergency platform, enables the generation of the security incidents, the natural disasters and the man-made disasters and the loss brought by the security accidents to be reduced, protects the economy, and maintains the sustained steady and coordinated development of the society. By establishing the security risk evaluation and early warning, the simulation system and the simulation method have the very important significance for improving the social public security emergency rescue of our country, the risk evaluation and the comprehensive management.