Abstract: Orange peel instrument, X-ray spectrometric thickness tester, scanning electron microscopy (SEM), three dimensional nano micro tester (FRT) were used to study the car door surface, Zn coating steel sheet, phosphate coating and original steel sheet from macro and micro aspects, the cause of stripe defects on the surface of car door was analyzed.The results showed that, when the production process of car was not changed, the micro sags and crests of surface during plating process mainly caused the stripe defects on the car surface.