The present invention relates to a method for preparing a diamond carbon membrane on a surface of stainless steel, including: immersing the pretreated stainless steel into a solution of a biomass-derived carbonaceous mesophase in ethanol for several minutes, prior to taking out and air drying; or alternatively, spraying the solution of the biomass-derived carbonaceous mesophase in ethanol onto the stainless steel surface, to provide a layer of the biomass-derived carbonaceous mesophase film adhered on the stainless steel surface upon full volatilization of the solution on the surface; and then carrying out thermal treatment under a hydrogen atmosphere, to prepare the diamond carbon membrane on the stainless steel surface. By the preparation process, which is convenient and easy in operation, and low in cost, the diamond carbon membrane can be made on the stainless steel substrate in a complicated shape, which has a high level of diamond phase and is uniform, dense, and firm in bonding with the stainless steel substrate, leading to improvement of corrosion resistance, wearability, rigidity and high temperature resistance of the stainless steel, and being worth expanding in practical application.