Abstract: The conventional shooting and bouncing ray (SBR) technique is mainly applied to electromagnetic (EM) scattering calculation for targets in the context of the free-space. When it is used for the EM scattering computation and SAR image simulation for the complex targets on rough ground surfaces, the calculation error increases especially at small grazing angles. To address the above problem, an improved SBR technique based on the four-path model is proposed, where the multiple reflections as well as the multipath scattering contributing to the total scattered field of integrated target-ground scene are taken into account. The integrated scene consists of the geometric models for the given target and its underneath rough ground slightly larger than the bounding box of target is firstly constructed. Next, the interaction scattering among target, ground geometry and the half-space interface is analyzed by the combination of the improved ray tracing technique and the quasi-image method. The scattering contribution for ray tubes is finally calculated using conventional high-frequency asymptotic methods. Results calculated by numerical method are used to validate the proposed technique. Simulated SAR images for typical targets on rough ground surface are presented and compared with the measured counterparts to demonstrate the usefulness of the proposed technique in high-fidelity SAR images.