The shortest path based on MAKLINK graph is composed of straight line segments, and there may have not sufficient space for path smoothing when the vehicle is bounded by turning radius. Both the necessary conditions that the vehicle makes a turn safely at the vertex of swell annulus and the space constraint equation of the path nodes are considered. Transition arcs can be employed directly to wipe off the inflexions of the path, which are intersections of the line segments on the shortest path obtained by the ACS algorithm. To speed up the convergence speed and avoid falling into local optimal solution, the ACS algorithm is improved in this paper by introducing the global-distance heuristic factor, using pheromone evaporation coefficient with the function of automatic adjustment and restricting the pheromone concentration within some range. The pheromone evaporation coefficient can adjust automatically. The simulation results show that the method can find a collision-free path quickly under different conditions. The quickness and feasibility are demonstrated.