Abstract: For resolving the operation complex and low setting success ratio of the convention hydraulic casing window sidetracking tool, we developed the KCZ140-J type mechanical casing window sidetracking tool. And the tool is including highly efficient mill cone, deflector and anchor packer. After borehole prepared completely, all the technology process of side drilling in casing is operated by once going in the hole (among them including the orientation, deflector, cutting window and fix window etc.). The structural characteristics of the tools, operating principle and the field usage situation are introduced. The reasonable construction of new anchor packer can ensure that the deflector will not descend or rotate when cutting window or normal drilling after cutting window under the condition of good cement quality in the original casing window position. This can cut down the cost of oil well sidetracking and increase successful rate and suggest to employment in each oil-field.