Abstract: Based upon the principle that when the distance between the draw well and its replenishment source, the influent stream,is mOre than 30 meters,the suspended matters,bacteria and partial chemical ions in the water will be filtered by the filter bed, it can be deduced that,replenished by either lateral influent stream or vertical perched water,the clean water will be obtained so long as it flows through a filter bed with a thickness more than 30 meters before it flows into the well. On the basis of this theory,the plan of waler supply for 756 plant is discussed herein.