Abstract: 2D rough surface model is used to study over the horizon radar EM scattering from the earth surface. The effective dielectric constants are calculated by semi-empirical formula in the cases of different temperature, humidity at given frequencies of HF band and microwave band. The 2D rough surface model is generated using Monte Carlo method with Gaussian spectral function to simulate the real earth surface. Surface integral equation is derived with the Tapered incident wave applied to eliminate the edge diffraction. PBTG/ SMCG algorithm is used to calculate the bistatic scattering coefficient. Studies have been done on over the horizon radar EM scattering from the earth surface. The study conclusion provides references for over the horizon radar remote sensing.