A magnetron sputtering scanning method for manufacturing a silicon carbide optical reflector surface modification layer and improving surface profile includes (1) for a silicon carbide plane mirror to be modified, first utilizing diamond micro-powders to grind and roughly polish an aspherical silicon carbide reflector with a conventional polishing or CCOS numerical control machining method; (2) after the surface profile precision of the silicon carbide reflector satisfies a modification requirement, utilizing a strip-shaped magnetron sputtering source to deposit a compact silicon modification layer on the surface of the silicon carbide reflector; (3) then, utilizing a circular sputtering source to modify and improve the surface profile of the reflector; and (4) finally, finely polishing the modification layer, and achieving the requirements for machining the surface profile and roughness of the reflector.