The flood calculation is based on flood risk map. In this paper, a 1D and 2D coupling numerical model of the Hanjiang River Flood Protection Area is established to evaluate the relationship between flow rate and water level, the water level and velocity of the feature points, the dam-break flood routing process. The results showed that the dam-break peak flow appears the largest at the beginning of the dam-breaking, as the water level in the reservoir falls gradually, the flow discharge decreases linearly from the top to zero till the 99h after dam breaking. The dam-break flood has a greater destructive power against the area at Xiangqiao district where the maximum velocity can be faster than 1.3m/s. Yunlu town, Denggang town and Xiangqiao district where the maximum inundated depths can be deeper than 2m due to the lower terrain.