In a known working environment,the three-dimensional global path planning of mobile robots is investigated in this paper.Firstly,both the updating strategy of global pheromone and the calculation method of pheromone increment in the ant colony algorithm are improved to make the planned path more reasonable.Next,the safety factor is introduced into the path planning and is calculated off-line in advance.Then,a fallback mechanism is designed to clear the pheromone of the point where ants fall into a deadlock,so as to achieve efficient obstacle avoidance of mobile robots in complex three-dimensional environment.Finally,the traditional search mode is improved to make the mobile robot move in the direction which is perpendicular to the main direction.Simulation results show that the above-mentioned path planning method is of a high searching efficiency with a shorter threedimensional path,and it is more practical.