This article studies an electrophoretic coating with a film thickness of 3~5 microns black epoxy cathodic electrophoretic coating that still imparts excellent coverage to the coated object within 3-5 microns.Explored the synthesis of tertiary sulfonium type dispersion resin and the preparation of the black slurry for black epoxy cathodic electrophoretic coatings;Analyzed the different influencing factors in the preparation process of black pulp.The experimental results indicate that the black epoxy cathodic electrophoretic coating with a film thickness of 3 microns still gives excellent coverage to the coated object,and the electrophoretic coating maintains a good appearance without yellowing and transparency.