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Regulated deficit irrigation (RDI) is one irrigation strategy that can conserve irrigation water and maintain yield. In this paper, we describe an investigation of the timing and efficacy of RDI in an experiment conducted in a waterproof shed on maize in 2009. Various levels of controlled soil water deficit, here expressed as the level of moisture in 30 cm soil layers, including high moisture content (70-75%), middle content (60-65%), and low content (50-55%). Grain yield increased along with evapotranspiration (ET), but the highest level of water use efficiency (WUE) was not consistent with the maximum yield. The amount of irrigation water under deficit conditions was usually between 269.4 mm and 342.7 mm in semi-arid areas. Mild water deficit at the jointing and flowering stages increased WUE by 24.38% and 23.02%, respectively, but decreased WUE by 19.07% at the grain-filling stage. Further differences were observed at the jointing stage (P<0.05). Water consumption intensity (WCI) was used to indicate irrigation timing and degree of RDI. The results of this study indicate that mild water deficit at the jointing stage is a better regulated deficit irrigation strategy for maize in semi-arid regions than deficit at other stages. It may be the optimal irrigation method for increasing maize production in semi-arid areas.