Abstract: Reference evapotranspiration was estimated by using Penman-Montieth(P-M) equation, Priestly-Taylor(P-T) equation and FAO-24 Blaney-Criddle(B-C) equation, and crop coefficient was also calculated by using the reference and actual evapotranspiration. Results show that the reference evapotranspiration calculated by using P-M equation is similar to that by using B-C equation, and the estimation calculated by using P-T equation is obviously lower than that of others. The crop coefficients calculated by using three equations are also significant different, and it is suitable using P-M equation and using B-C equation during April to October according to the annual change of crop coefficient. However, the crop coefficient calculated by using P-T equation is remarkably higher than that of others. The irrigation demands were also estimated based on the crop water requirements and rainfall which were significant different in difference rainfall years. The irrigation demands range is from 270 mm to 400 mm and 0 to 330mm for winter wheat and summer maize, respectively.