Purpose:Accurate image reconstruction strongly depends on the information of the scan geometry of the cone beam CT(CBCT),which is difficult to obtain in practical machine without precise geometric calibration.A practical geometric calibration method on prototype CBCT was proposed in this paper,aiming to provide a practical geometric calibration tool for practical applications.Methods:The geometry calibration method consists of 6 steps:1)Simple phantom design and manufacture with easily accessible materials; 2)Fast analytical geometric calibration to estimate the initial geometry parameters; 3)Iterative calibration algorithm for searching the optimal parameters around the initial estimation and correcting the unrealistic hypothesis of the analytic algorithm; 4)FDK reconstruction using the geometry calibrated projections.In addition,a sharpness function was performed to evaluate the gradient of the reconstructed image and eliminate blur artifact caused by image segmentation.The method was validated by simulation data and practical Phantom in prototype CBCT.Results:Comparing with the current analytical method,the simulation result showed the proposed method reduced the relative error of the horizontal coordinate of projection center in the detector from 2.42%to 0.23%,and the error of roll angle of the detector from 0.83%to 0.53%,which indicates that the proposed method is more precise and robust.In addition,the calibration results of practical phantom showed no obvious distortion or blurring,proving the high efficiency and efficacy of the proposed method.Conclusions:A practical geometric calibration method of CBCT was developed,which was fully tested and well implemented with high precision and accuracy.