Abstract: To understand the mechanisms of agricultural N₂O emission, we investigated the N₂O emission dynamics, the N₂O isotope signatures, and the site preference value under different soil water conditions in the vegetable farmland of North China, by using the stable isotope technique and the acetylene inhibition method. The results demonstrated that N₂O emission was significantly affec-ted by the water condition, and N₂O emissions from soil with water-filled pore space (WFPS) of 70% were significantly higher than that with 50% WFPS. N₂O emission occurred mostly in the early stage of fertilization, and decreased rapidly in the later stage of fertilization. At 50% WFPS, nitrification was the major process generating N₂O during the early fertilization stage, accounting for approximately 90% of the N₂O emission. However, the contribution of nitrification decreased sharply, whereas denitrification became the dominant process, accounting for 80% of the N₂O emission 7 days after the fertilization. On the other hand, at 70% WFPS, denitrification was the main process releasing N₂O during the early fertilization stage, decreasing from 70% to 40% and then gradually increasing to 80% 10 days after the fertilization. Overall, N₂O emission was mainly dominated by the denitrification. The effect of different water treatments on soil nitrification and denitrification took place mainly in the early stage of fertilization, and N₂O emission was gradually dominated by the denitrification at the later stage. These results suggested we could reduce N₂O emission by approp-riately reducing the amount of irrigation in the vegetable farmland of North China.