Water brake technology has great significance on monorail rocket sled test, which coupling nonlinear process between high-speed flow impact and structure response. In this paper Finite element method(FEM) and Smoothed particle hydrodynamics(SPH) model is used to analyze the braking force performance and the structure response during the monorail rocket sled braking process. The results show that the FEM-SPH method has high accuracy, which braking force error between numerical simulation and experiment is 3.92% when velocity of rocket sled is 750m/s. The safe braking distance of numerical simulation is 100m, while the real distance of experiment is 105m. The error between numerical simulation and experiment is just about 5%.