This paper proposes a fast coupled iterative algorithm for calculating the complex three-dimensional scattering of rough dielectric surfaces and conductive targets. The algorithm is designed for practical composite electromagnetic scattering models and establishes a coupled iterative integral equation system for the rough surface and target. Iterative calculations are performed until the specified accuracy is achieved. To improve computational speed, Physics Based Two Grid-Sparse Matrix Canonical Grid (PB-SM) acceleration algorithm and a hybrid domain basis function based on quadratic surface modeling are applied using the fast Method of Moments (MoM) for fast computation. The effectiveness of the fast coupled iterative algorithm is verified by comparing the results with those of high-precision MoM calculations. During the calculation process, error iteration curves are plotted to show that the error can be reduced to 10 −6 after 10 iterations, and the convergence rate meets the requirements of practical calculations. Based on the algorithm proposed in this paper, several examples are calculated, and the scattering variation of targets in different environments is mainly studied, and suggestions are given to improve the accuracy of target detection and identification in complex environments. The results of the study have some significance for ultra-low altitude target detection, precision strike, stealth and anti-stealth.