A high-precision method was investigated to realize the geometric calibration of half-cover scanning in circular cone-beam Computed Tomography (CT). First, projected areas of steel balls were segmented from the background by using the Otsu′s method, and the mass centers of balls were calculated. Then, the elliptic functions for mass centers were fitted by the least-square algorithm, and the rotation angle of detector was determined by Cho′s geometric calibration method for circular scanning. Finally, the rotated mass centers were fitted as two ellipses, and the rest geometric parameters except the tilted angle of detector were calculated by using Noo′s geometric calibration method for circular scanning. Experimental results indicate that the measuring precisions of rotation angle and skew angle for the detector are 0.02 °and 0.01°,respectively, the measuring precisions of source-detector-distance and source-object-distance are 0.05 mm and 0.01 mm, respectively; and the calculating precisions of orthogonal projection coordinates of source are 0.07 mm and 0.15 mm. The proposed method depress the geometric artifacts significantly, and can satisfy the demands of high-precision image reconstruction.