The embodiment of the invention discloses a method for cleaning silicon nitride on the surface layer of a graphite base plate. The method comprises the step of cleaning the graphite base plate in a cleaning tank by using a hydrofluoric acid solution until the silicon nitride is removed from the surface of the graphite base plate, wherein the silicon nitride is coated on the surface of the graphite base plate. According to the method, the silicon nitride is removed by a chemical method, namely the silicon nitride is cleaned by utilizing the chemical reaction of the hydrofluoric acid and the silicon nitride. The hydrofluoric acid does not react with the graphite, so the graphite base plate is not influenced, the original physical property of the base plate is maintained, and the service life of the base plate is not shortened.