The MPS (Moving Particle Semi-implicit) method has been proven useful in free-surface hydrodynamic flows. Despiteits applicability, the MPS method suffers from some shortcomings such as non-conservation of momentum and spuriouspressure fluctuation. By introducing new formulations for pressure gradient and new formulation of source term ofPoisson Pressure Equation, we have proposed modified MPS method, namely CMPS-HS (Corrected MPS with HigherorderSource-term) method, for the prediction of wave impact pressure on a seawall. The improved performance of theCMPS-HS method is shown through the simulation of wave impact problem in comparison with the experimental data.