The canopy-air temperature-difference models, RW = a + b (Tc-Ta), for wheat, corn and cotton, and the soil-air temperature difference model, RW = a' + b'(Ts -Ta), for bare soil were developed based on the data observed in Handan area in 1990 and 1991. The average relative error was less than 20%. The models are simple and easy to be used for irrigation management and drought monitoring over large areas. The method of crop coverage calibration for the canopy temperature and the temperature-difference indexes of the drought grades were also presented in this paper.