Abstract: In order to solve the technical difficulties of sidetracking with ϕ139.7 mm casing in shallow horizontal wells of the Jidong Oilfield, which included high pumping pressure, low ROP, poor oil-water layers isolation effect, and rapid rise of water cut after the oil well was put into production, etc., many countermeasures were taken. Those technologies include adoption of ϕ79.4 mm non-standard drill pipe to lower the mud pump, adoption of a small size hydraulic pressurization and speed-up tool that can flexibly pressurize the drill bit to increase the ROP, selection of ϕ95.3 mm non-standard casing, adoption of the top cementing completion with expansive suspension liner and screen liner, and formulation of technical measures to improve the cementing quality of slim hole sidetracking. The key technologies for drilling and completion of shallow slim hole sidetracked horizontal wells in the Jidong Oilfield was thus formed. These technologies were tested in 5 shallow sidetracking horizontal wells with high water-cut in the Jidong Oilfield. Compared with adjacent wells without adoption of these technologies, the pumping pressure was effectively controlled, the ROP was increased by 24.6%, the drilling cycle was shortened by 14.1%. At the same time, the poor sealing problem of the slim hole with a narrow gap was solved, and the isolation of the aquifers in horizontal section and seal of the sidetracking window was achieved, by which the impact on the later oil production was avoided. The test results showed that the proposed key technologies could effectively increase the ROP in the slim hole sidetracking in horizontal wells, shorten the drilling cycle and isolate oil and water layers. With good effect in speed-up and efficiency improvement, the technologies have a high potential for popularization and application.