Abstract: A mathematic model of soil evaporation based on water surface evaporation by using the method of energy balance equation and microclimatology was established to precisely estimate the soil evaporation. The results show the parameters such as the diurnal maximum and average temperature in the water surface and drying soil surface, diurnal water surface evaporation, and wind speed are involved in the model. The verified results of the model indicate that the theoretical values fit well with measured ones (R2=0.90). The complex physical process of soil evaporation is avoided in the model for the introduction of reference evaporation surface, which makes the soil evaporation be easy to be calculated.