A method of manufacturing carbon coated aluminum foil as a cathode of solid aluminum electrolytic capacitors Comprising the steps of: preparing an aluminum foil by setting the aluminum foil into a chamber; roughening at least one surface of the aluminum foil by introducing gas into the chamber and activating an electric field so that the gas is ionized and turned into a plasma; and depositing carbon atoms by introducing gas mixed with carbon atoms and turning on the electric field again so as to make the carbon atoms have positive charge thereby impacting into and attaching firmly to the rough surface of the aluminum foil to form a carbon film.