Abstract: Well Hai14-20 is a multilateral well with three branches, and it is the first trial to conduct the window milling using our self-designed tools and by our own experience.Some of the important issues for window milling in a multilateral well are described, such as its planing, the window milling technique, setting of the whipstock,window protecting, etc. It focuses on an important tool used in the multilateral well, the retrievable whipstock, and its recovery, its setting and arrangement technologies are further discussed.