Abstract: Irrigation water use efficiency (WUEi) reflects the efficiency of irrigation of crops. It’s a key criterion for evaluation of agricultural production level, irrigation project condition and irrigation management level. Based on the full irrigation survey data, the WUEi of main crops of United States and China was analyzed through classify calculation and weighting methods. The average WUEi of grain, tuber crops, forage, cotton is about1.98, 8.90, 2.54 and 0.26 kg/m3, respectively. The WUEi of above four kinds of crops under sprinkler irrigation is 2.26, 9.44, 3.20 and 0.36 kg/m3, respectively. But the ones under surface irrigation is 1.55, 6.96, 2.15, 0.23 kg/m3, respectively. The average WUEi of corn, wheat, rice in 13 states of United States are 2.94,1.24 and 1.39 kg/m3, while the ones in 226 lagre and moderate irrigation districts in 10 provinces of China are 2.04, 1.19 and 0.80 kg/m3. The main reason of the low WUEi in China is the backward irrigation technique and lower water use efficiency of the irrigation districts which caused by less water saving irrigation area.