Abstract: A field experiment was conducted characterize denitrification and N2O emission from soil under optimized nitrogen fertilization in winter wheat-summer corn rotation system in North China using acetylene inhibition-intact soil core incubation technique. Results showed that there were significant seasonal variations of denitrification rate and N2O emission flux during winter wheat-summer corn growth periods, and positive correlations existed between inorganic nitrogen concentration (NH4+-N, NO3--N) and denitrification rate. Total denitrification losses and N2O emission amounts from soil in winter wheat-summer corn rotation system were observed to be reduced with decreasing of N application rate, and which in winter wheat season were found to be less than those in summer corn season. Total denitrification losses and N2O emission amounts under conventional N fertilization were respectively 1.62 and 1.67 times as high as those under optimized N fertilization during winter wheat growth periods, and 2.01 and 2.00 times during summer corn growth periods, which N application rate decreased by 30% and postponing N application as compared with conventional N fertilization with an application rate of N300 kg/hm2. Therefore, postponing N application could reduce denitrification losses and N2O emission through modifying soil inorganic nitrogen concentration.