Abstract: Long sections of irregular boreholes in the Triassic and Carboniferous formations lead to poor cementing quality of the ?177.8mm liner in Tahe Oilfield, Xinjiang, thus a combination displacement cementing technology of turbulent and plug flow is proposed to solve this problem. By selecting the suitable drag-reduction agent and adding proqer dosage in the cement slurry, and controlling the rheological property, the combination displacement can be practiced. The consistency coefficients of cement slurry for turbulent-plug flow displacement under various flow rate and casing diameters are derived, and the density designing values for cementing fluid, flushing fluid and spacing fluid are also proposed. Field using of this technology in well TK427 shows that it can greatly improve the cementing quality.