The utility model discloses a damping device for a crossbeam of a cargo truck. The damping device comprises a buffering cushion support produced from macromolecules through injection moulding, wherein the buffering cushion support comprises a first connection plate; a limit plate connected with the first connection plate to form an L-shaped structure is arranged at the bottom of the first connection plate; the first connection plate is in fastening connection with the inner wall of the crossbeam through a first fastening bolt; the limit plate is arranged against the inner side of the bottom of the crossbeam. The damping device has the advantages of being simple in structure, convenient to produce, low in cost, and capable of effectively enhancing the longitudinal rigidity of the crossbeam and increasing torsional moment of the crossbeam.