In this paper, the potential evapotranspiration and agricultural water demand are calculated, and the agricultural water demand is compared with water resources in Beijing. The results indicate that water resource can meet the requirement of agriculture in normal climatic years, although a deficiency would appear in drought years. At present, a higher potential could be found of water saving in agriculture over Beijing areas. If the potential is fully taken into account and the necessary measures are carefully adopted, the water could meet the requirement by agriculture even in drought years.