Abstract: In order to study the dynamic performance of a helicopter traction system on deck, and analyze the factors influencing its motion stability, a dynamic model of the traction system was developed. In the model, the inertial force of the helicopter traction system produced by coupled roll-pitch-heave motion of the ship hull and the influence of variable vertical load on the tire cornering stiffness were considered. Based on this model, a 4 degree-of-freedom (DOF) perturbation equation with periodic coefficient was obtained, and the motion stability of the traction system was analyzed by the Floquet theory. The results show that the critical velocity of the traction system, compared with that on land, reduces sharply above sea state 2, with a magnitude not less than 70%; the traction motion stability increases as the mass ratio of helicopter to tractor decreases and the cornering stiffness of the tractor rear wheels increases.