The high water level and long duration of flooding in the river increase the risk of dam break and overflow floods, and when the dam bursts, the threat will be enormous. Hence then, the risk analysis of the dam break and overflow floods is of great necessity for the real-time management of flood control. Considering the influence of the Qingtongxia reservoir, we use lateral connections to build the two-dimensional coupling model of channel and conservation area in this article to simulate the flood process of the river in the Ningxia section of the Yellow River under the design of once-a-century flood water. Meanwhile, based on the GIS platform, the index of flood damage quantified by flood collapse assessment is obtained, which provides a reference to the flood managers and economic constructors to formulate reasonable flood plans.