Abstract: In order to understand the displacement mechanism and improve displacement efficiency in highly deviated well,three-dimensional annular model was developed using the CFD software Fluent,and numerical simulation studied with drilling fluid displaced by cement slurry by means of VOF method.The paper studied the influences of deviation angle,casing eccentricity and density difference between cement slurry and drilling mud on displacement efficiency and stability of displacement interface.The simulation results indicated that wellbores with a high deviation angle have lower displacement efficiency;in an eccentric annulus at highly deviated section,the displacement efficiency first increases then decreases with the increase of density difference between cement slurry and drilling fluid;casing eccentricity is not absolutely a factor reducing displacement efficiency in highly deviated well.A certain casing eccentricity (eccentricity 0.1-0.2 proposed) can eliminate fingering caused by the density difference to some extent in narrow annulus at lower side,and improve displacement efficiency.After numerical simulation study on cement displacement,the displacement mechanism differences between highly deviated wells and vertical wells were identified,which provides reference and basis for optimizing displacement parameters in the design of cementing for highly deviated wells.