A three-dimensional numerical model based on the potential theory was developed to study the oblique wave action on vertical walls. A source term inside the domain was used to generate incident waves and outgoing waves were dissipated by sponge layers and trans- mitted by radiation boundaries. The finite difference method was used to solve the governing equations and boundary conditions in the regular transformed domain in σ-coordinate. Satisfactory agreements between the numerical predictions and experimental results of wave force were obtained. It is concluded that the maximum wave force acting on the vertical walls is induced by the obliquely inci- dent waves rather than the normally incident waves. A three-dimensional numerical model based on the potential theory was developed to study the oblique wave action on vertical walls. A source term inside the domain was used to generate incident waves and outgoing waves were dissipated by sponge layers and trans- mitted by radiation boundaries . The finite difference method was used to solve the governing equations and boundary conditions in the regular transformed domain in σ-coordinate. It is said that the maximum wave force were obtained. the vertical walls is induced by the obliquely inci- dent waves rather than the normally incident waves.