The invention discloses a preparation method of a porous carbon electrode material, and belongs to the field of preparation of new energy materials. The electrode material for a lithium-air battery, which is relatively small in particle size, uniform in granularity and free of agglomeration is prepared by microwave drying, carbonization and modified treatment of selected residues after tobacco stem extraction or other residues after plant extraction as raw materials. A reactant has the advantages that the raw materials are easy to obtain, the cost is low, the reaction conditions are easy to control, the yield of a product is high and the result repeatability is good; and the electrode material is of a porous structure, and is relatively small in particle size, uniform in granularity, large in specific surface area (946.85-1572.31m<2>/g) and free of agglomeration.