The ant colony algorithm has two disadvantages: slow convergence and precocity. Aiming at the disadvantage of slow convergence speed, this paper proposed a new kind of pheromone named Directed Pheromone. Using the Directed Pheromone to enhance the pheromone trails on the shorter arcs in order to speed the algorithm's convergence. Besides, a new parameter is proposed to select arcs with low pheromone trails. Examples of TSP are used to compare the improved ant colony algorithm with basic ones. The simulation experiments show that the improved algorithm has faster convergence speed and more precise calculation results.