Generally, the geometric error of CNC milling machine has a great effect on the synthetical precision of a machine tool. In this paper, the measuring and compensating technologies of the geometric error of CNC milling machine were investigated. The measurement, model and compensation of the plane error field in the working space of high-speed CNC milling machine were discussed systematically. The basic feature of the geometric error was verified by using the high accuracy linear grating along the single axial direction experimentally. Following, the backlash compensation algorithm of the synthetical geometric error of interpolation movement and the evaluation system of position accuracy were proposed for the backlash during CNC milling machine processing. The result indicates that the basic feature of error is established and provides a basis for putting forward the new error measurement method under the essential measuring condition. The backlash could be well compensated.