Abstract: It is very important to study the dynamic response of elastic-plastic structures when it enters the water for structural safety design and stability evaluation. However, there is still insufficient research on elastic-plastic deformation, cushion effect, and three-dimensional effect when the structure enters into water. The Smoothed Particle Hydrodynamics (SPH) method has unique advantages in dealing with this problem because of its meshless and Lagrangian properties. Therefore, the water entry of the elastic-plastic structure based on the SPH method is studied. Based on the improved fluid and elastic-plastic structure coupling SPH model and the Riemann contact algorithm, the water entry of the two-dimensional elastic-plastic wedge with solid-liquid coupling is studied, and the effects of velocity, elastic modulus, and yield stress on the dynamic responses of the wedge such as slamming force, deflection, and yield location distribution are analyzed. Based on the improved SPH method with the addition of the air model, the gas-solid-liquid coupling water entry of the two-dimensional elastic-plastic wedge is studied, and the influence of air cushion effect on the response of the wedge is analyzed. Based on GPU parallel technology, the three-dimensional water entry of the elastic-plastic wedge is studied, and the influence of three-dimensional effect is analyzed. The results show that, compared with the elastic wedge, the peak value of the slamming force on the elastic-plastic wedge is reduced, and the relationship between the peak value of the slamming force and the velocity and the elastic modulus is more complex. There is a positive correlation between the volume of air cushion and the buffering. When the water entry velocity is less than or the deadrise of the wedge is greater than a certain value, the effect of air can be ignored. The three-dimensional effect can significantly reduce the slamming force, and its peak value is about 74.9% of that of two-dimensional results.