In the high frequency of microwave, sea surface or ship target usually has the characteristics of electrically large size and very sophisticated structure, which imposes a huge computational burden for the electromagnetic modeling of the composite ship-sea scene. To simplify the calculation, based on the facet-model theory, the graphical electromagnetic computing method and the four path model, a hybrid method for the electromagnetic scattering computation of electrically-large composite ship-sea scene was presented. Under the precondition of guarantee calculation precision, the efficiency was improved obviously. The radar cross section of time-varying sea surfaces and ship target for different radar parameters were simulated and analyzed. The results show good agreement with the experimental data and the accurate numerical results, which demonstrates the correctness of the method. Application of the model to synthetic aperture radar imaging of marine scenes was developed. Simulation results demonstrate the effectiveness of the proposed method.