According to the formula recommended by the Grain and Agricultural Organization of UN for calculating the quantity of heat radiation of crops, the quantity of water needed by the vegetable crops in the flatland area of Zhangjiakou is calculated. The results from the demonstration fields show that drip irrigation under mulch is the best way for saving water,spraying irrigation the second, then piping irrigation. The meteological service for mediating and controlling watersaving irrigation, giving the quantities of average waterneeding irrigation and irrigation in different watersaving patterns, is described. The results show that the irrigation, according to the water needing of crops and meteological conditions, can save water by 40% without investment, while engineering watersaving, combined with meteological service, can save water by 40% to 70%, which is the most economical way for saving water.