Aiming at the fluctuation problem of milling machine processing accuracy in actual production of enterprises,the Renishaw XL30 laser interferometer was used to carry out precision detection and compensation experiments on the positioning error of the MVC850B CNC milling machine.The environmental parameter comparison test was carried out to obtain the factors affecting the measurement of positioning error;the influence of input variables such as feed speed,processing time and measurement distance on the backlash and pitch cumulative error was determined by three-factor dual-index orthogonal test to judge the primary and secondary relationship of each input variable;the change of backlash and pitch cumulative error under the influence of a single factor was obtained through single factor comparative test.The semi-closed loop feedforward compensation method was used to compensate the positioning error of CNC milling machine,and the workpiece processing verification experiment was carried out.The results show that by using the proposed error compensation method,the machining accuracy of workpiece can be effectively improved.