Abstract: The sidetracking drilling technology of casing internal oblique device is the most widely used sidetracking technology in China, and it is also the most mature technology. However, there are also various problems in the using process. The top deformation of the whipstock, the irregular window, and the steering of the whipstock are all likely to cause the resistance of the trip through the window. In this paper, by drawing on the experience of other sea and land oilfields, combined with on-site judgment, the complex situations of drilling through the window point blocked by the deformation of the top of the whipstock in a well in East China Sea is successfully handled, which provides reference and inspiration for the treatment of similar problems.