Abstract: When the radar target is located near a rough surface, a composite scattering consisting of self scattering, surface scattering, and multiple scattering between the two will occur. The calculation process of this composite scattering is relatively complex. To address this, first of all, the influence of surface roughness on the electromagnetic scattering of the target is analyzed, and the equivalent electromagnetic current and the scattering cross-section as the core analytical quantities are identified in this paper. Next, the radar reflection coefficient of rough surface is calculated, and its impact on the equivalent electromagnetic current is analyzed. Finally, an analytical expression for the diffraction field strength is established using the diffraction coefficient and diffusion factor, and then the important parameters of scattering cross-section, including the surface-element scattering field, edge diffraction field, and multiple scattering field, are calculated. Simulation results show that increased roughness leads to a more complex and non-uniform distribution of current density, thereby altering the flow pattern, directionality, and intensity distribution of the equivalent electromagnetic current. At the same time, roughness also significantly changes the electromagnetic scattering intensity and radar cross section (RCS); at most scattering observation angles, the scattering intensity attenuates continuously, and the RCS decreases synchronously, ultimately weakening the received radar echo intensity.