Abstract: An enclosed intermittent vent method was adopted to determine ammonia volatilization (AV) from soil of winter wheat-summer corn rotation system in North China. Results showed that AV from soil in both winter wheat and summer corn growing season occurred mainly within 14 days after fertilization, and the cumulative AV amount from fertilizer N in winter wheat growing season was found to be less than that in summer corn growing season. Cumulative AV amounts from soil of winter wheat-summer corn rotation system were observed to be reduced with decreasing of N application rate. Total AV amounts under conventional fertilization were 2.28 and 2.03 times as high as that under optimized N fertilization, where N application rate was decreased by 30%. Compared with conventional fertilization (N 300 kg/ha), the N rate was decreased by postponing N application, but the grain yield was significantly increased. Therefore, 30% of nitrogen fertilizer could be expected to be saved by optimized fertilization, and postponing N application is a rational and practicable N fertilization method for reducing AV in winter wheat-summer corn rotation system.