The wave forces on an artificial island standing on the sea‐bed are investigated by the proposed hybrid method. A boundary integral equation is developed for the inner fluid domain encompassing the arbitrarily shaped island, while an eigenfunction expansion is used to represent a simple velocity field in the outer fluid domain. Applying the natural boundary condition on the matching surface, the wave force and moment on the wetted surface of the island are found according to the calculated velocity potentials. A gravity step circular dock is used as a test case to confirm the present computation. As a practical application of the present method, numerical results for an elliptical artificial island are presented.