Based on field experiments with randomized complete block design in a semi-arid location in Gansu Province,the study examined the effects of the timing and amount of supplementary irrigation on potato yield and water use efficiency(WUE).The result shows that supplementary irrigation at the growth stages had significant impacts on potato yield and WUE.Potato yield and WUE in supplementary irrigation treatments were all higher than those of the controls.The highest yield and WUE achieved in the experiments were 19 178.57kg/hm2,which is 21.77%than that of the control,and 52.7kg/(hm2·mm),respectively.Compared with the traditional way,supplementary irrigation improved significantly the yield characteristics: higher percentage medium and large tubers,more tuber number per plant,and higher yield per plant.In addition, the results also indicate that budding stage was the most sensitive time of the potato responding to supplementary irrigation,and the optimal supplementary irrigation amount was 3kg per plant at the budding time.This would be a better cropping management considering both water-saving and high yielding for potato cultivation in semiarid areas.