The results of the experiment conducted in the semi-arid area of central Gansu showed that the yield and water use efficiency(WUE) of wheat/corn compound colony could be improved by supplementary irrigation with catchment rainfall.The marginal predominance of wheat was obvious,and there were insignificant differences among the treatments.According to the results of yield,WUE and IWUE,the best cropping and supplementary irrigation pattern was determined for semi-arid areas.