The geological conditions are complex with large lithology difference and stratum pressure difference in Tahe oilfield, there are local high pressure brine zone and gypsum salt bed, the hole size is restricted, which bring many technical difficulties for drilling engineering. Aiming at these problems, sidetracking by setting whipstock, directional ream while drilling, expansion tube and slim-hole horizontal well drilling technology were put forward. TK7-640CH drilling practice shows that the above technologies are feasible in the application for φ177.8mm casing whipstock sidetracking horizontal well in ordovician of Tahe oilfield, can seal complex formation and the abnormal pressure system. The paper discusses and analyzes the feasibility of the technical difficulties and technical schemes in sidetrack drilling; sums up the successful experience in real drilling, which provides technical support for the recovery and regeneration for old wells in Tahe oilfield.