Abstract: With the increase of oil feld exploitation, sidetracking from old well is an important technology for stable production in oilfeld. In numerous sidetrack drilling technology, open hole sidetracking with horizontal well is the most effcient way. There are many diffculties with this sidetracking technology. In this paper, the successful practices in Bohai Oilfeld have been discussed, including the sieve tube cutting and fshing technology, horizontal reservoir cementing plug technology and narrow window sidetracking, which have been used to overcome the technical diffculties. In addition, these series of technologies can also be widely used in the wells with similar situations in other felds. These series of technologies can reduce the drilling and completion operation risk and cost, being important technical ways for reducing cost and increasing effciency in adjusting wells.