Abstract: Ammonia volatilization (AV) from soil is an important pathway for fertilizer N loss from field, while less information is available on AV from black soil in Northeast China. For understanding the seriousness of AV in this area, a venting method was used to investigate AV from black soil in maize monoculture system, treatments of nitrogen fertilizer (Urea) application included: (1) N0 (Control, no nitrogen application); (2) N1 (N 150 kg/hm2); (3) N2 (N 225 kg/ hm2); (4) N3 (N 300 kg/ hm2).The N3 represented the traditional N application, and for N1, N2, and N3, 1/2 was used before sowing as basal, and 1/2 used at jointing stage as top-dressing. One more treatment was added as N4 (N 225 kg/ hm2), 1/3 the total amount was used respectively before sowing, at jointing stage，and at booting stage, and this represented optimized N application approach. In field condition，it was found that ammonia volatilization lasted short，and took place within a week after N application. The amount of AV from N fertilizer as top-dressing was found to be higher than that as basal, due to the higher temperature and the lower soil moisture at jointing stage and booting stage. The N loss through AV increased with the application rate of nitrogen fertilizer. For N1, N2 , N3 and N4 treatment, the amount of AV from N fertilizer were N 5.09, 9.18, 13.47 and 7.14 kg/ hm2，which were equivalent to 3.39%, 4.08%, 4.49% and 3.17% of fertilizer N applied, respectively. Optimized N application approach lowered the N loss by AV greatly compared to traditional N application. Therefore, optimized fertilization is of great importance for increasing N use efficiency and saving N fertilizer in intensive cropping area in Northeast China.