The calibration target board is the necessary material in the camera calibration. For the influence of the distance between the camera and the target calibration object on the calibration accuracy, the image of the checkerboard is about 1/3, 1/2, 2/3 of the whole screen The experiment illustrate that the calibration accuracy is highest when the chessboard chat is about 1/3 of the screen. To quantify the influence of the accuracy made by the virtual calibration plate, the virtual calibration plate with size of 9×7 or 13×9 was designed, and executed the calibration under the condition which the virtual calibration plate is about 1/3 of the screen. The results prove that virtual calibration is superior to the real calibration board with same specification.