Abstract: At present, the accuracy design remains at the level of the designer's sensory experience, and the developed error sensitivity analysis cannot provide direct quantitative guidance for accuracy design. In view of the above problems, the error increment equation was first established based on the theory of the multi-body system. Meanwhile, the prediction model of component tolerance and geometric error source parameters was constructed. Furthermore, a method of error sensitivity analysis based on component motion was proposed. Taking CA swing head five-axis NC milling machine as the subject, and taking "S" specimen as the object of processing, the error sensitivity analysis of five axis machining center was carried out by using the method of error sensitivity analysis based on the increment of machine tool component motion. The experimental results show that the sum of the error sensitivity coefficients of the six error source parameters ε_y(x)、q₆^e、ε_x(x)、q₅^e、θ_C^e and ε_zx⁴⁵ is 0.95 and the sum of sensitivity coefficients of other error source parameters is only 0.05. Therefore, this method can effectively identify the key parts that affect the machining accuracy of CNC machine tools, and lay a theoretical foundation for improving the machining accuracy of CNC machine tools.