Abstract: The effects of nitrogen fertilization on activities of leaf xanthine oxidase(XOD),superoxide dismutase(SOD),catalase(CAT) and the content of H2O2 and MDA were studied in two winter wheat cultivars(irrigated cultivar and dryland cultivar).The results showed that N supplication promoted leaf CAT and SOD activities;while depressed XOD activity and reduced MDA content,among which it had the most striking influence on N180.Moreover,the highest yield was obtained for N180.Therefore we could conclude that N 180 kg/ha was the recommended application rate for the winter wheat production at the local condition.Comparing to irrigated cultivar,dryland cultivar had higher SOD and CAT activities and lower XOD activity and MDA content under N0 treatment,thereby,the tested items could be adapted to(evaluate) the drought resistance of winter wheat,furthermore,rational nitrogen supplying could promote leaf CAT and SOD activities and decrease XOD activity and MDA content.So that N could improve drought-tolerance ability through increasing the ability of leaf membranes superoxidize resistance. We could conclude that rational application of nitrogen could enhance the drought-tolerance ability by decreasing the MDA and H2O2 content,and increasing SOD and CAT activities.