Abstract: Owing to the failure of improving single well productivity due to the problem that segmented fracturing can’t be effectively conducted in horizontal well with ϕ88.9 mm hole sidetracked by using the old wellbore in water flooding low permeability sandstone reservoir, numerical simulation method is used to simulate the influence of different fracture density and number of fracturing sections on oil well productivity and water cut based on the well pattern arrangement and remaining oil distribution characteristics. The laboratory simulation and field test result show that when the fracture density is 4–6 per 100 m and the fracture length is 100–120 m, the effect of water control and oil increase is better. The effective separation of each fracturing section in horizontal section of slim hole can be fulfilled and the efficiency can be improved by using segmented multi-cluster fracturing technology with soluble bridge plug technology and pony packer pipe strings. Successful practice of segmented multi-cluster fracturing technology in slim hole sidetracking horizontal well provides the technical support for low permeability reservoir to recover single well productivity and to improve ultimate oil recovery.