Since its predominant anti-erosion,cathodic electrophoretic coating has been widely used in automotive coating industry.This paper focused on the crater defect in an automobile coating production line.Through a series of experiments and analyses,the causes was find that bubbles were attached to the lower surface of hood and roof,and difficult to detach from the surface.The defect was eliminated by the way of adjusting the direction of some nozzles used for tank surface flow and tank bottom circulation.The study has.a guiding significance for the design of electrophoretic coating equipment in the future.