Abstract: When milling complex parts such as thin-walled blades and S-specimens by five-axis machine tools, the coupling effect of machine tool geometric errors on machining quality is complex, which cannot be directly mapped to the specific contour surface, resulting in insufficient compensation pertinence. Aiming at this problem, a mapping method of geometric error and specimen contour error is proposed. This method constructs a geometric error transfer model and inversely solves the tool contact length corresponding to the section height. Combined with Sobol global sensitivity analysis method, the sensitivity ranking of error terms is realized, and the coupling relationship mode between the two error terms is further considered to form a priority compensation strategy. The experimental results show that compared with the compensation method only for a single error term, the coupling compensation strategy improves the qualified rate of contour error by 21.88%, which verifies its engineering value in the identification and compensation of key coupling errors.