Abstract: To address the challenge of predicting electromagnetic scattering characteristics of electrically large targets in a maritime atmospheric duct environment, this paper proposes a hybrid computational method combining the three-dimensional parabolic equation method (PE) and the physical optics method (PO). In this approach, the PE is employed to solve the propagation of electromagnetic waves in the background environment, while the PO is used to calculate the scattering of radar waves by the target. Additionally, a plane wave spectrum decomposition technique is introduced to facilitate the efficient integration of the two algorithms. The proposed method is validated through scattering simulation experiments involving a metallic sphere over a flat surface, where it is compared with results from the multilevel fast multipole algorithm (MLFMA) and the PO method. Finally, the proposed method is applied to predict the electromagnetic scattering of a ship target under evaporation ducts of varying heights. The results demonstrate that the proposed PE-PO method effectively accounts for the influence of atmospheric ducts on both the incident wavefront and the target scattering process, providing a novel technical approach for analyzing and understanding the electromagnetic scattering characteristics of electrically large targets in ducting environments.