Abstract: To study the scattering mechanism of radar terrain returned in vertical incidence region, an experimental program to measure the scattering coefficients of terrain including farmland and sand in vertical incidence region was carried out by using S and 8mm Linear Frequency Modulated Continuous Wave Radar scatterometers. A terrain scattering return database connected with radar frequency, altitude, antenna pattern, incidence angle, and the roughness and permittivity of ground surface was established. The return data processing approach is provided, the theoretical scattering model of rough terrain surface is derived, and then the measured data is fitted by the model. The experimental results show that the measured scattering coefficients agree with the given model, the radar cross section per unit area at vertical incidence of sand is 2~3dB larger than that of farmland, and the scattering coefficients at 8mm is 18~20dB larger than that at S frequency-band.