Abstract: Within the framework of integral equation method, a hybrid approach using equivalent principle is proposed to solve electromagnetic scattering problems. This theoretical model can resolve different relative position of target and the half space surface, including target at either side of the half space surface or the target straddling the surface. Apart from traditional methods using half space Green function to solve scattering problem concerning the existence of half space, the method in this paper uses free space Green function of the two dielectrics which form the half space. Therefore, Somerfield integral can be avoided and be compatible with fast algorithms (MLFMA etc.). Basic theory of equivalent principle is introduced. In this method, an infinite surface is truncated into a finite one, a therefore, tapered incident wave is used to avoid the edge effect. The far field response of a target with a half space background should be expressed as a differential radar cross section. Numerical examples show good agreement with the reference and simulation result from FEKO. The proposed method here can be a tool to analyze the effect of half space on the target nearby.