High fertilizer N application rate and low nitrogen use efficiency are two typical problems in vegetable farming systems in China. To explore quantitatively relationship between N₂O emission rate and fertilizer N application rate and its mechanism, and effect of nitrification inhibitors in mitigating N₂O emission, a field experiment was carried out having four crops of vegetable and lasting one year. Results show that when the N application rate varied in the range of 0~1 733 kg hm^-2 a^-1, the total N₂O emission increased exponentially with N application rate, no matter with or without the addition of any nitrification inhibitor, that is to say, the higher the N application rate, the higher the N₂O emission rate. The application of nitrification inhibitor reduced N₂O emission (8.75%~25.28%) from the soils of all the N fertilization treatments, and the mitigation effect increased with N application rate. In plots applied with N 300 or 400 kg hm^-2 season^-1, the economic benefit arising from reduction of N₂O emission as a result of the use of the nitrification inhibitor was higher than the cost of the nitrification inhibitor. Therefore, the use of nitrification inhibitors is a profitable option even without considering some other factors like improving N use efficiency.