A deformation defect was found on the surface of the pressing edge of the back of front door assembly for a certain car which was reviewed as a Bclass defect both in the white body and the complete vehicle of AUDIT, and the appearance quality of the complete vehicle was affected. Then, the defect in assembly was analyzed, and it was found that the surface deformation of the outer panel, the springback of the inner panel and the gap between pressing edges when hemming the outer and inner panels together resulted in the defect above. After trying out for many times, the defect in front door assembly couldnot be eliminated or relieved by optimizing the surface deformation of the outer panel and controlling the springback of the inner panel. Furthermore, the rectification on hemming die was executed by reverse compensation method, and the defect was improved significantly. Finally, Cclass defect in AUDIT was obtained, and the goal of improving the complete vehicle quality was achieved, which provided a reference method for solving similar problems in new car model.