This experiment was conducted during February to June 2012 in Demonstration farm of Arba Minch University located in the central rift valley of Ethiopia. The aim was to investigate the effects of different levels of deficit irrigation imposed at different growth stages of maize (BH-140) crop on its development, grain yield and water use efficiency. AquaCrop model was calibrated and validated using field experimentation data. The crop water requirement of maize for full irrigation application was calculated using CropWat 8.0. The water application levels considered were 100% of crop evapotranspiration (ETc), 75%ETc, 50%ETc and 25%ETc. based on these irrigation levels and four growth stages of maize crop, ten treatments were arranged. These treatments were replicated three times. Data collected during the experiment were: crop biomass, soil moisture content, irrigation depths and final yield. The result showed that the highest yield was found in treatment six, T6 (8842 Kg/ha) which was subjected to water deficit during mid- and maturity-stages; whereas minimum yield of about 5264 kg/ha was obtained under T8 which was irrigated imposed to deficit during the whole growing season except during the initial stage. The highest (2.11 kg/m3) and lowest (0.93 kg/m3) water use efficiency was recorded under T8 and T4. Generally, water deficit of 50%ETc during third and fourth growth stages had no significant effect on the grain yield of maize and it is worthwhile to save irrigation water during these growth stages. The model performed well in simulating the growth of aboveground biomass, grain yield, and canopy cover (CC) for most of the treatments but it was less satisfactory in simulating the growth performance of treatments under prolonged water-deficit. The fact that the AquaCrop model is easy to use, requires less input data, and its sufficient degree of simulation accuracy make it a valuable tool for estimating crop productivity under deficit irrigation, and on-farm water management for improving the efficiency of water use in agriculture. Key words: Deficit irrigation, growth stage, maize, crop water productivity, AquaCrop.