A method for removing ash from a solid carbon material: Reaction conditions are mild, and ash may be removed more effectively. The ash removing method comprises: S1) mixing an alkaline sub-molten salt medium and a solid carbonaceous material to be treated, heating so that alkali and ash in the solid carbonaceous material to be treated react in the alkaline sub-molten salt medium, and performing solid-liquid separation on a mixed slurry resulting from the reaction to obtain a first solid product and an alkali treatment solution, wherein in the alkaline sub-molten salt medium, the mass fraction of the alkali is greater than or equal to 50%; S2) using an acid solution to perform acid cleaning treatment on the first solid product, and performing solid-liquid separation again to obtain a second solid product and an acid cleaning solution.