In order to provide ＂high quality＂ optimal path for the user of navigation systems,a mathematical model of the optimal path with multiple quality constraints is proposed.Then,to solve this model,local pheromone update rules and global update rules of the ant colony algorithm are re-designed,a pheromone update operator is introduced to increase the pheromone on the optimal path dynamically,and a heuristic factor of visibility is improved.As a result,an improved ant colony algorithm is generated.Simulated results demonstrate that the improved ant colony algorithm is of good optimization ability and rapid convergence,and that it helps to accurately find the optimal path meeting multiple quality constraints in the road network.