The field study of crop response to water stress is important to maximize yield and improve agricultural water use efficiency in areas where water resources are limited. This study was carried out during two growing periods in 2009 and 2010 in order to study the effect of water stress on crop growth, water consumption and dry matter yield of silage maize (Zea mays L.) supplied with flood irrigation under the semi-arid climate of Tadla in Morocco. Four to five irrigation treatments were applied at the rates of 100, 80, 60, 40 and 20% crop evapotranspiration (ETc) of maize. Soil water status, crop growth, leaf area index and above-ground biomass were measured. Results showed that irrigation deficit affected plant height growth, accelerated the senescence of the leaves and reduced the leaf area index. The maximum values of this parameter reached at flowering under the full irrigation treatment (100% ETc) were 5.1 and 4.8 in 2009 and 2010, respectively. Dry matter yields varied from 5.3 t·ha-1 under T4 (40% ETc) to 16.4 t·ha-1 under T1 (100% ETc) in 2009, whereas in 2010, it oscillated between 3.9 t·ha-1 under T5 (20% ETc) to 12.5 t·ha-1 under T1 (100% ETc). The establishment of the water budget by growth phase showed that the water use efficiency was higher during the linear phase of growth. Water use efficiency calculated at harvest varied between 2.99 kg·m-3 under T1 to 1.84 kg·m-3 under T5. The actual evapotranspiration under T1 (100% ETc) was 478 mm and 463 mm in 2009 and 2010, respectively. Using the averaged values of the two years, linear relationships were evaluated between dry matter yield and water consumption ETa. The yield response factor (Ky) for the silage maize for both growth seasons was 1.12. Under the Tadla semi-arid climate, it is proposed that silage maize should be irrigated as a priority before other crops with a Ky lower than 1.12. It is also recommended that, under limited water supplies, irrigation be applied during the linear phase of growth of this crop.