The invention belongs to the field of manufacturing and processing of a graphite material, and particularly relates to a graphitizing method and a graphitizing device of a graphite product. The graphitizing method of the graphite product comprises the following steps: preparing a furnace body, paving the bottom of the furnace body, surrounding a furnace core, padding a bottom pad layer, assemblinga product, filling with a resistance material, covering a top pad layer, covering a reaction material and a heat-insulating material, performing power transmission and cooling. According to the method, a plurality of Acheson graphitizing furnaces are connected in parallel and power transmission is conducted simultaneously. By the graphitizing method of the graphite product, the graphite product with high quality and high yield can be obtained, the comprehensive productivity is improved and the electric energy is saved.