Abstract: Field experiment was conducted in wheat /maize/potato intercropping system at the cheng zhuang station in JingTai in 2003;Accordingly,tube simulating experiment was done by using the 30cm diameter PVC tube in wheat/maize intercropping system in the net house of Gansu Agricultural University in 2003.The results were showed that crop root grew deeper and crop yield increased with light water deficit (60%-65%).Under the condition of serious water deficit ,root fresh weight and crop yield in intercropping system reduced significantly. Fresh root weight of wheat and maize under the treatment of phosphorus application were 94.66% and 67.67% higher than those under the no phosphorus application treatment at the jointing stage of wheat (seedling stage of maize); 42.08% and 124.13% at the stage of milky stage of wheat (male tetrad stage of maize); 61.61% and 82.58% after harvesting of wheat (milky stage of maize ).From field experiment ,it were also indicated that crop economic yields got to the highest under the treatment of middle irrigation (W2:P1050m3/hm2) and high phosphorus (P2:150kgP2O5/hm2).