Abstract: To solve the problems of poor ability in perception and dynamic response, and slow action in decision-making for the evaluating and pre-warning system of the urban flood disaster, a digital twin city model including five modules of Physical Entity, Virtual Entity, Services, Digital Twin Data, and Connection was developed based on the digital twin technology. The evaluating and pre-warning system based on the digital twin city model of the urban flood disaster was analyzed as follows: the system framework was interpreted by describing the basic components and the functions of the five modules; focusing on three key technologies of the visual representation, the data-driven model, and the intelligent closed-loop control in virtual-real interaction, the technical framework of the digital twin city was analyzed; the construction method of the system was illustrated from four processes of constructing the digital model, integrating data, simulating scenario, and making decision. The evaluating and pre-warning system based on the digital twin city model of the urban flood disaster can perform the functions of monitoring and warning automatically, commanding and dispatching timely and intelligently.