The spatial error is the most important factor affecting the machining accuracy of turning and milling compound CNC machine tools.The positioning accuracy of each axis of the existing machine tools is not improved effectively.Therefore,a modeling and compensation methods for the spatial error of turning and milling compound CNC machine tools were designed.Ignoring the position independent errors of the two rotating axes of the machine tool,the geometric error identification model of the machine tool was constructed through homogeneous coordinate transformation theory,and the geometric error identification model was simplified to realize the geometric error identification of the two axes.In the workpiece coordinate system,according to the results of geometric error identification of the rotation axis,the spatial error model of the machine tool was constructed using the multi-body theory.Based on the error model,the synchronous spatial error compensation strategy was designed by using the ideal inverse kinematics,and the compensation values of each axis were calculated by iteration to realize the compensation of spatial error.The test results show that the positioning accuracies of X axis, Y axis and Z axis of the experimental machine tool are improved by 0.6 μm after the compensation of the designed method.The positioning accuracies of axis B and axis C are improved by 4″and 3″respectively,the repeated positioning accuracy of each axis is greatly improved,and the roundness of the reverse stroke test of the machine tool is also improved.