Abstract: Smoothed particle hydrodynamics (SPH), a smooth particle dynamics method based on Lagrangian description is good at numerical simulation of flood discharge with drastic changed free surface. However, the SPH method usually uses uniformly distributed particles to discretize the computational domain of the fluid in space. For engineering problems, the particles numbers and calculation complexity are large. In order to break through the application scope of SPH method in practical large-scale computing issues, the parallel acceleration of SPH method was realized by the mixed programming technology of C++ and CUDA and the help of GPU hardware equipment. Through calculating the flow passing issue of smooth spillway composed of three arc segments of WES, the accuracy and reliability of GPU-based SPH method in this paper are verified. The computational efficiency is 61.8 times higher than that of the original SPH simulation process. Finally, the GPU-based accelerated SPH method was applied to the discharge simulation of hydraulic engineering, the flow characteristics of smooth spillway and stepped spillway were simulated respectively. By observing the variation process of the free surface and the velocity distribution along the discharge section, the effect of the step on the discharge phenomenon is analyzed.