A telescopic hydraulic cylinder is used in the mechanism, among which the hydraulic cylinder forming the rotating pair with the upper connecting rod is used for lifting, and the other hydraulic cylinder is used for closing the tail plate. The connecting rod and the closed cylinder form a parallelogram mechanism to ensure the translational movement of the tail plate; after the telescopic movement of the hydraulic cylinder is converted into the swing movement of the connecting rod, the lifting of the tail plate is relatively stable; the structure of the mechanism is compact in the vertical direction. When being lifted to the upper limit position, there is still a certain distance between the bottom end of the mechanism and the ground, which does not affect normal transmission. Therefore, the mechanism meets the design requirements.