Abstract: Given technical problems such as drilling difficulties for conventional window sidetracking tool strings when the well section has a large dogleg angle, and it is easy for the cone milling shoe to deviate from the guide slope, and for the whipstock to run separately from the milling shoe, a whipstock set by choke pressure difference and matching tools including a secondary milling shoe, a flexible coupling sub, and a window milling shoe were developed. Further, a BHA (bottom hole assembly) for one-trip casing window sidetracking was thereby created, and it accomplished the desired whipstock running, whipstock setting, and window sidetracking. A one-trip casing window sidetracking was divided into five stages, and recommended milling parameters were provided for each stage. Technical measures were formulated to deal with complications during the implementation process, and a suite of robust one-trip casing window sidetracking technologies was developed. These technologies were then applied in 203 wells in Bohai Oilfield for casing window sidetracking, with an average window sidetracking period of 10.5 h, a window repairing period of 2.6 h, and a successful window sidetracking rate of 100%. The average window sidetracking time of these wells was 2.4 h shorter than that of wells adopting two-trip window sidetracking technologies, with an efficiency increase of 22.8%. The field application showed that with higher window sidetracking efficiency and a lower drilling cost, the proposed one-trip casing window sidetracking technologies could provide technical support for offshore oilfields to stabilize production and enhance the degree of recovery.