The error sources that affected the accuracy of machine tool were needed to be identified and the error compensation was needed in order to improve the positioning accuracy of NC machine tools. The use of laser interferometer principle of CNC lathe precision for testing was discussed. The mathematical model of the detecting data processing was established, and the compensation process of positioning accuracy error was settled. The positioning accuracy was detected and analyzed combining to the specific NC turning lathe. According to analysis, the error compensation of opposite clearance and thread pitch was realized. At last, the evaluation of positioning accuracy compensation effectiveness was carried out. The practical application indicates that this positioning accuracy detection and compensation process is feasible, and the positioning accuracy of NC machine is improved significantly.