Abstract: A nonlinear time-domain coupled numerical model is adopted in order to calculate the nonlinear wave forces acted on a box-shaped ship in harbor. A higher order nonlinear term is also included in the equations in order to extend the model to a fully nonlinear problem for shallower water waves. The whole domain is divided into an inner domain and an outer domain. The inner domain is the area beneath the ship hull, which is governed by the Euler equations. The outer area is the area between the ship and harbor walls, which is governed by the higher order Boussinesq equations. A relevant pressure physical experiment was conducted to validate the model, and a good agreement is obtained between the numerical results and the experimental data. The numerical computations of the model are simple and efficient, which is particularly useful for the computation of the non-linear wave forces on a ship in a harbor.