The invention discloses a novel reciprocating type belt sander contact roll structure which comprises a rack, a contact roll and a proportional roll. The contact roll is arranged on the upper portionof the rack, and the proportional roll is arranged on the lower portion of the rack. The novel reciprocating type belt sander contact roll structure is characterized in that the contact roller is connected with a contact roll swing mechanism and a contact roll rotating mechanism. Aiming at the defect that according to an existing common belt sander theory, chromatic aberration is prone to be generated, and the polishing efficiency is low, original polishing of the contact roll only in the circumferential rotating direction is changed into bidirectional composite polishing of circumferential rotation and axial fast reciprocating motion. The contact does not only do circumferential motion during polishing, axial reciprocating motion is added, and the polishing efficiency (the throwing trackof each sand particle on a sanding belt is changed into a face from a line) is improved; and the machined part surface chromatic aberration generated after polishing is carried out is reduced, and thesurface quality is improved.