The invention relates to a method for preparing battery-grade manganese sulfate by separating nickel, cobalt, lithium and manganese from battery black powder. The method comprises the following steps: 1) slurrying the battery black powder, adding concentrated sulfuric acid, performing first-stage agitation leaching, controlling the pH value to be less than 1.5 and the temperature to be 85-95 DEG C, and adding a reducing agent; (2) carrying out filter pressing on the first-stage leachate, removing iron and aluminum from filtrate by adjusting the pH value, and then carrying out extraction treatment to separate manganese, cobalt, nickel and lithium, and taking filter residues as raw materials for second-stage leaching; 3) carrying out second-stage reduction leaching on filter residues produced by the first-stage filter pressing, adding the reducing agent, controlling the pH value to be less than 1.5, and controlling the temperature to be 85-95 DEG C; (4) carrying out filter pressing on the leachate, and washing filter residues to obtain graphite residues; 5) adding barium sulfide into the filtrate subjected to second-stage filter pressing, controlling the temperature to be 55-70 DEG C and the pH value to be 3.5-4.5, and reacting for 1-3 hours; (6) carrying out filter pressing on the nickel and cobalt removed solution, wherein the filtrate is a manganese sulfate solution; and 7) adding sodium dimethyl dithiocarbamate and sodium fluoride into the manganese sulfate solution, and carrying out filter pressing to obtain the battery-grade manganese sulfate solution.