The practical applications of two types of calibration method to CCD camera's image center measurement were researched. With regard to image center,pixels' distribution on image plane is still symmetrical even under the influence of lens distortion. Based on this,in direct optical method,the image center is judged by the symmetry of pixels' position in vertical and horizontal directions on image plane. In lens distortion based perspective projection method,a complete imaging model could be constructed and image center is one of the parameters in the model. Two kinds of main lens distortion are considered in the model. Tests were done and the comparison was made for two methods. The second method's strong convergence property was confirmed.