In this paper, the shooting and bouncing ray (SBR) method combined with the physical theory of diffraction (PTD) is applied to solve the composite electromagnetic (EM) scattering of a ship located in an island region. The digital elevation model (DEM) containing terrain information of the region is used as the geometrical model. The distribution of landforms in DEM is extracted from satellite images utilizing image annotation tools. The island model is derived by combining DEM terrain data with landform distribution. Limited by the DEM resolution and the loss of sea state information, the sea part of the aforementioned island model is replaced by a simulated sea surface. Finally, the recombined island model is used in investigating the scattering mechanism of a ship in island background. By comparing the results, it can be concluded that the intensity of composite scattering mainly comes from the specular reflection of the island background in the mirror direction and the coupling effect of the ship in the backscatter direction.