Abstract: Irrigation and fertilization are the two most important methods to increase crop growth and yield. Understanding the water consumption characteristics and grain yield of oat (Avena sativa) under different water-nitrogen (N) regimes is useful to optimize oat cultivation. In the 2014-2015 oat growing seasons, field experiments were conducted with three irrigation levels and three N application rates to study the effects of the water-N interaction on soil water consumption in the 0-150 mm layer, soil evaporation, grain yield, and water use efficiency (WUE) of the oat variety ‘Longyan 3’. The three irrigation amounts were 270 (I₁), 337.5 (I₂), and 405 mm (I₃) and the three N application rates were 90 (N₁), 120 (N₂), and 150 kg/ha (N₃). The soil evaporation and the proportion of soil evaporation (E) to evapotranspiration (E/ET) decreased and then increased during the growing period. Under the same N application rate, E and its proportion of E/ET increased with increasing amounts of irrigation from the jointing to the filling stage, but decreased from the filling to the harvest stage. The oat water consumption and grain yield under a fixed N application rate were positively related to the amount of irrigation, whereas WUE was negatively related to the amount of irrigation. The highest grain yield of oat was in N₃I₃ (5466.0-5727.5 kg/ha), followed by N₃I₂ (5428.5-5678.5 kg/ha), and then N₁I₁ (4504.5-4804.3 kg/ha). The highest WUE was in N₃I₂ [(12.11-12.82 kg/(mm·ha)], followed by N₃I₁ [12.04-12.63 kg/(mm·ha)], and then N₁I₃ [9.79-10.58 kg/(mm·ha)]. The water-nitrogen interaction had significant effects on WUE and oat yield. Our results suggest that N application at 150 kg/ha combined with irrigation at 337.5 mm is a water-saving method to cultivate oat with high-yields in the Northwest Oasis area.