The invention provides a preparation method of a three-dimensional sulfur-doped graphene / sulfur composite material electrode slice. The preparation method comprises the following steps of step (1) mixing and grinding graphite oxide and benzene disulfide, then placing in a nitrogen protection muffle furnace for reacting, and naturally cooling to room temperature after reaction to obtain sulfur-doped graphene; step (2) adding polyacrylonitrile, the sulfur-doped graphene and graphite oxide into N-methyl pyrrolidone, performing ultrasonic reaction, then coating an aluminum foil with mixed slurry, and drying to obtain an electrode slice; step (3) placing the obtained electrode slice into a muffle furnace protected by inert gas, slowly heating to 400 to 500DEG C, and naturally cooling; step (4) completely inserting the electrode slice obtained in the step (3) into a Na2S2O3 solution, slowly dripping hydrochloric acid into the solution, and drying to obtain a positive electrode slice. The electrode slice prepared by the preparation method provided by the invention can be directly used for a cathode of a lithium sulfur battery without adding any conductive agent and bonding agent, so that the cost of the electrode is greatly reduced.