Abstract: Centralizing the casing string in borehole is the importantprerequisite for improving the cementing displacement efficiency. In this paper, the mechanical analyses of the casing strings with centralizers have been made respectively in the straight-inelined and the curved boreholes, and the boreholes crooked with changed azimuth. The action of hydraulic pressure in the borehole is pre cisely considered. Both the deflecton of the casing itself and the displacement of centralizers have been studied.