The flood of Shuxi Flood Protection Area in Yishusi Basin has the characteristics of mountainous flood, which has the characteristics of high water level, short duration and small flood volume. The accurate calculation of dike break flood process is the key and difficult point of flood analysis in flood protection zones. In order to accurately simulate the flood process and its evolution in the reserve, a one and two-dimensional dynamic coupling hydrodynamic model has been established. The one-dimensional model was calibrated and verified by the measured flood data in 1993, 2003 and 2012.The two-dimensional model of flood protection area and Luoma Lake has been corrected and optimized by regional investigation and survey. The real-time interactive process of water flow between river channel and nature reserve has been simulated by coupling calculation, which can be used as the calculation platform of flood submergence factors. Taking Matou breach of Yihe River as an example, the flood duration of the breach is 13.2 h, the peak flow is 537 m3/s, and the flood volume is 8.33×106 m3. The velocity of flood in the protected area is fast, the flood inundated area is 107.7 km2. It is proved that the breach flood of Matou will evolve along the Baima River to the downstream. People and property could be transferred and resettled by the submerged water depth, flood path and arrival time.