In this paper, an automatic calibration system for binocular stereo imaging based on Zhang's 2D flat calibration method is proposed. Firstly, the interface of system is designed. After images being collected, the result of Harris corners detection extracted from the 2D flat are displayed on the interface, meanwhile, the system begins to compute intrinsic and extrinsic parameters of the stereo camera and then optimizes them by maximum likelihood estimate. Finally, mean reprojection error and the visualization of camera intrinsic parameters shown on the interface is convenient for users to analyze factors of effecting stereo camera calibration.The results appear that the proposed system not only operates easily but also obtains high precision of calibration, which improves the traditional method of camera calibration.