The invention provides a method for improving specific volume of an electrode aluminum foil for a solid-state capacitor. 0.5-1.2wt% of Na<3>PO<4> is added to phosphoric acid pretreatment; an aluminum foil is placed in a phosphoric acid mixed solution at a temperature of 50-90 DEG C and is reacted for a certain time to form Na<2>HPO<4> on the surface of the aluminum foil, so that oil stains, impurities, and dirty on the surface of the aluminum foil can be removed more completely; and the aluminum foil can be more uniform in the subsequent hole expansion in multiple times, and the hole expansion rate is improved, thereby achieving an effect of improving specific volume.