Abstract: Abstract: Water shortage and excessive application of nitrogen fertilizer are two prominent problems in the agricultural production system globally. Finding new ways to improve the efficiency of water and nitrogen fertilizer use is of great significance to the realization of sustainable agricultural development. Oxygenated water is an efficient and non-pollution irrigation water treatment technology. The application of oxygenated water in the irrigation in agricultural production can improve the soil environmental conditions and promote crop growth. In this study, the objective was to investigate the effect of oxygenated water on soil nitrification under different water contents. The oxygenated water was produced by a rapid generation device of micro-nano bubbles, and the dissolved oxygen concentration in water was monitored to reach 20 mg/L. Silt sandy loam soil sampled from the Xinjiang cotton production area was incubated with ammonium sulfate as additional substrate under controlled conditions in the laboratory. Either ordinary water or oxygenated water was added into soil to obtain different soil moisture conditions (30%, 60%, 100% and 175% of Water Holding Capacity, WHC). During the incubation, soil samples were taken and NH4+-N and NO3--N contents were analyzed on day 0, 1, 2, 4, 6, 8, 12, 16 and 20. The nitrification kinetic equation and nitrification intensity were used to quantitatively evaluate the dynamic change characteristics of NH4+-N and NO3--N content over time. The initial consumption rate of NH4+-N, the maximum consumption rate of NH4+-N, the time to reach maximum consumption rate and the average production rate of NO3--N from each treatment were analyzed and compared. The results showed that the nitrogen transformation of the studied silt sandy loam was dominated by nitrification. During incubation, the NH4+-N added into soil was consumed, and almost depleted in all treatments except the ones with 30%WHC; The NO3--N was produced simultaneously. For both the ordinary water and the oxygenated water treatments, with the increase of moisture content, the soil nitrification intensity first increased to the maximum at 100%WHC, and then decreased. Under different soil moisture conditions, oxygenated water treatment affected the soil nitrification intensity to varying degrees. Compared with ordinary water treatment, oxygenated water promoted nitrification most significantly under the condition of 60%WHC, the maximum consumption rate of soil NH4+-N increased by 8.9%; the peak occurrence time was earlier, and the average generation rate of NO3--N increased. Under the condition of 100%WHC, no significant difference was found in the consumption of NH4+-N in the oxygenated water treatments, and only the average generation rate of NO3--N increases by 1.58 times. Under the condition of 175%WHC, the maximum consumption rate of NH4+-N in the soil decreased by 21.5% and the peak occurrence time lagged; and the average generation rate of NO3--N did not change obviously. This research proposes the most suitable water condition for the promotion of soil nitrogen transformation by oxygenated water, which provides an important theoretical basis for the development of agricultural efficient water and fertilizer utilization technology.