The invention discloses a preparation method of a ferric-carbon internal electrolysis filler; the preparation method comprises the steps of taking cold-rolled oil sludge and pulverized coal as raw materials, mixing the raw materials evenly, then carrying out dry distillation under the protection of inert gas to obtain iron-doped activated carbon, and thus obtaining the ferric-carbon internal electrolysis filler. The iron and steel industry common pulverized coal and cold-rolled oil sludge are sintered into iron-containing activated carbon particles comprising micron-sized iron and reduced iron components, and a pore forming phenomenon appears in ferric-carbon internal electrolysis filler particles, so that the reaction efficiency of a primary battery is improved and the cost is low.