In order to improve the path planning efficiency and security based on traditional Hybrid A* algorithm, an improved Hybrid A* path planning algorithm is proposed and applied to a tractor-trailer mobile robot system. Firstly, the heuristic function is improved to reduce the computation in the path planning process, so as to improve the planning efficiency. Secondly, the obstacle penalty function is designed, which in turn realizes the avoidance of obstacles on the travel path in advance and avoids getting into local optimal solutions in U-shaped obstacles. Finally, Because the tractor-trailer model cannot be considered as a prime point, a collision detection algorithm is used to improve the reasonableness and accuracy of the planned path. The simulation results show that the improved Hybrid A* path planning algorithm can be applied to the tractor-trailer mobile robot system, and has the characteristics of high planning efficiency, high security and smooth path, which provides a theoretical basis for its path planning in practical application.