Based on the study of status quo of agricultural water resources utilization in Northwestern Ecological Zones, this paper analyzed the water utilization potential and increasing production potential at the theoretical level by the method of AEZ. The results are: the whole Northwestern Ecological Zone is suffered from the shortage of water resources; Its current water use efficiency is low and the waste is as serious as shortage; Water is key to exert the biomass and maximum potential yield of crops. If the water use efficiency rises up 10%～20%, the land production potential will be surmounted greatly.