Aiming at the problem that two-dimensional hydrodynamic model is too time-consuming to be applied in a large-scale area or case with fine resolution for the urban flood simulation, an urban inundation model was constructed by coupling the SWMM model and the LISFLOOD-FP model. Then the GPU-based parallel computing technology was adopted to accelerate the constructed inundation model. Taking the flood simulation of urban area in Xiangshui County of Yancheng City as an example, the efficiency of the parallelized algorithm was analyzed. The results show that the GPU-based parallel computing technology can significantly improve the model efficiency, and the parallelized model could simulate a 12-hour flood event in 8 minutes at 5 m resolution, which can be used for quick response to urban flood emergencies. The efficiency of the parallelized algorithm was more obvious at a higher spatial resolution, and the highest speedup of 10. 86 times was achieved at 2 m resolution. In order to maximize the computing efficiency of GPU, a large amount of computation is required in each time step, and the additional time caused by frequent data transmission between host and GPU should be minimized.