Abstract: The Yaohu Lake dyke flood protection area in Poyang Lake region has various water systems and complicated hydrological condition. The inundant flood hits the entire region during the flood period, so the corresponding flood risk analysis in this region has a great significance. A 1D and 2D coupled hydrodynamic model to simulate the evolution of levee-breach flood is developed in this study, and the model is optimized by roughness partitioning and river topography reduction, which improves the model's precision. The system is applied to Yaohu Lake dyke flood protection area, and the calculation area is divided into unstructured triangular grids. The instantaneous dike break is set up, and the breach flux meets the principle of water balance. The evolution result is reasonable and reliable, based on which the flood risk analysis is carried out. The analysis results show that the areas flooded due to the breaches of Jimingzhou, Dawangmiao and Sijiazha are 10.62, 56.67 and 18.36 km² respectively. The submerged distribution basically follows the principle of topography, and the submerged water depth in the protected area is basically deeper than 3 m. And the inundated area size and the impacted population are related to the breach's position.