Abstract: ZhuangHai Well 8Ng-H3 is developed by commingled production in the whole screen section, leading to high water-cut of the well. To keep on exploring GuanTao reservoir layer, the extended-reach horizontal well ZhuangHai Well 8Ng-H3k is sidetracked from the well. The sidetracked casing was ?244.5 mm by size, and was sidetracked with whipstock sidetracking and rotary navigation technology. The vaiable density screen was taken as the completion method to control the bottom water. The well obtained an oil rate of 25 t/d and water-cut of 6.3%, and the water control effect is obvious comparing to the adjacent producers. The success experience of the treatment on the well supplies a valuable case for the same type wells.