In this paper,appearance issue after E-coating in the commissioning of thin-film pretreatment process was focused,The optimization of the body plate grinding method,the optimization of silane pretreatment and the optimization of electrophoresis tank fluid were fully tested.The causes of the problem are analyzed and verified in depth.Solutions are put forward from the aspects of silane pretreatment process daily mainte nance,parameter optimization and electrophoresis parameter optimization.