A method is presented for separable compensable and uncompensable geometrical error sources between the tool and workpiece of computer numerical control (CNC) machine tool. According to compensable errors, the compensation model was built. The compensable geometrical errors was measured by squareness errors direct identification using laser interferometer and prism square. The calculation formula for compensation quantity was derived. The compensation experiment was carried out on geometrical errors compensation module of SIEMENS 840DNC system. The decrease rates of 8 indexes of geometrical errors were 165%~92% after compensation. The compensation effect was satisfied. The results show that the technology of modeling and compensation for compensable geometrical errors of machine tools is effective and feasible, which is suitable for different types of machine tools.