The working principle is as follows: One traction seat support is arranged on the lower side of the seat cover plate made of steel plate, and the pin shaft is connected with the seat cover plate, and the base of the traction seat can be rotated forward and backward with the pin shaft as the center. The bottom surface of the traction base is connected with the pulled trailer by bolts. A locking mechanism consisting of a horseshoe, a diagonal iron, a knuckle, an adjusting plate, a cross bar, a tie rod and a spring is arranged under the seat cover, and the horseshoe is fixed at the seat. On the cover plate, the knuckle, the tie rod and the cross bar are connected by a pin shaft, and the inclined iron is also connected by a pin shaft, and the pull rod is connected by a spring to the rib plate below the seat cover plate. It is characterized in that the two tails behind the saddle-shaped seat cover are large arcs, and the middle has a butterfly-shaped concave surface, which divides the entire plane into five similarly sized portions.