Underframe fixing device for supporting box body

The utility model discloses an underframe fixing device for supporting a box body. The underframe fixing device comprises a supporting bottom plate, the sliding truss is connected with the supporting bottom plate in a sliding manner; the pulley assembly is connected with the lower part of the sliding truss; wherein the supporting bottom plate comprises sliding grooves, and the sliding grooves are symmetrically formed in the two sides of the upper surface of the supporting bottom plate; the limiting protruding blocks are symmetrically arranged on the upper portion of the inner wall of the sliding groove. The sliding wheel assembly comprises a sliding wheel, the sliding wheel is matched with the sliding groove, and the sliding wheel abuts against the lower surface of the limiting protruding block. According to the embodiment of the utility model, the pulley assembly is arranged at the bottom of the sliding truss and then is in sliding connection with the sliding groove in the supporting bottom plate, so that th