The invention discloses an atmospheric corrosion exposure test fixture and an atmospheric corrosion exposure test method for a small-sized metal material. The fixture comprises an insulated bottom plate and an insulated cover plate, wherein the insulated cover plate is mounted on the insulated bottom plate; a plurality of square metal samples are clamped between the insulated bottom plate and the insulated cover plate; the insulated bottom plate comprises a bottom plate main body and a square bottom plate groove; the square bottom plate groove is formed in the middle of the bottom plate main body; a plurality of bottom plate bumps are uniformly and symmetrically arranged on two long sides of the bottom plate groove; the insulated cover plate comprises a cover plate main body and a square cover plate groove; the square cover plate groove is formed in the middle of the cover plate main body; a plurality of cover plate bumps are uniformly and symmetrically arranged on two long sides of the cover plate groove. The metal samples can be conveniently and easily clamped between the insulated bottom plate and the insulated cover plate. Moreover, groove openings are formed in the middles of the insulated bottom plate and the insulated cover plate, and the bumps which are used for clamping the metal samples are arranged at the groove openings, so that the contact area between the fixture and the metal samples can be as small as possible, and the influence on the metal samples in the exposure test process caused by the fixture is reduced.