Abstract: The accuracy of dam break flood propagation simulations is pivotal for the effectiveness of reservoir flood predictions. This study introduces a numerical simulation method, specifically tailored for dam break flood propagation analysis, using the smooth particle hydrodynamics (SPH) method. Through the establishment of breach particles and a particle library, the particle state was adjusted based on Riemannian invariants. Consequently, an improved SPH dam break propagation model with specific boundary conditions was developed. The spatial initialization of particles in the SPH model was transitioned to boundary initialization, facilitating the integration of the breach flow process with the SPH method at the breach boundary. Using the Malpasset dam failure as a case study, the model's accuracy in simulating dam failure floods was examined. The outcomes indicated that the model's precision was commendable, aligning well with recorded measurements. Additionally, when the model was employed to simulate the flood propagation forecast of a particular reservoir dam failure, it was used to determine the submersion depth and flood process experienced by downstream channels. The findings revealed that when the upstream reservoir experiences extraordinary flood and overflows the dam, the peak flood elevation at the channel's inverted siphon remains below the check flood level. The improved SPH model exhibited high accuracy, robust reliability, and efficient integration with the breach calculation model, making it a viable method for dam break flood propagation.