Abstract: Research on the electromagnetic environment on ships that are mounted with many electric systems and equipment are of vital importance on improving the electromagnetic compatibility and protection capability. First， the physical theory of diffraction（PTD） algorithm is verified with simplified models, which can be used to calculate the target shaded area and edge diffraction field when calculating the scattered field. Then， the physical optics（PO） and PTD are combined to calculate the field around the ship illuminated by electromagnetic waves. Next， the results are compared to the MIL-STD-461C standard, and the hazard areas of the ship are estimated, revealing that the superstructure is the major hazard area. Finally, the ray tracing from the source to the view point beside the mast is obtained with the method of geometrical theory of diffraction(GTD)， which successfully explains the potential threat of superstructures: the electromagnetic wave that impinges on the structure of the ship will be repeatedly reflected. In brief, the combination of a variety of algorithms for the studying of the ship electromagnetic compatibility has a great significance.