A simulated database built with the Dobson semi-empirical model was fitted to the Hallikainen formula by the least square regression method. The coefficients at key frequency points of SAR were calibrated with some improvement. The simplified model between the real part of the complex permittivity and the soil volumetric moisture content was established. It was validated and compared with other models. The results show that the simplified model has better accuracy than the Hallikainen empirical model, and also has good accuracy and practicality compared with the complex Dobson semi-empirical model.