Based on the characteristics of parallel dispensers in automated picking system,an order-picking optimization problem is presented.Firstly,the working principle of parallel dispensers is introduced,which implies the time cost of picking each order is influenced by the order-picking sequence.So the order-picking optimization problem can be classified as a dynamic traveling salesman problem (TSP).Then a mathematical model of the problem is established and an improved max-rain ant system (MMAS) is adopted to solve the model.The improvement includes two aspects. One is that the initial assignment of ants depends on a probabilisfic formula instead of a random deployment;the other is that the heuristic factor is expressed by the extra picking time of each order instead of the total.At last,an actual simulation is made on an automated picking system with parallel dispensers.The simulation results proved the optimization value and the validity of improvement on MMAS. Based on the characteristics of parallel dispensers in automated picking system, an order-picking optimization problem is presented. Firstly, the working principle of parallel dispensers is introduced, which implies the time cost of picking each order is influenced by the order-picking sequence. So the order-picking optimization problem can be classified as a dynamic traveling salesman problem (TSP) .Then a mathematical model of the problem is established and an improved max-rain ant system (MMAS) is adopted to solve the model. The improvement includes one is that the initial assignment of ants depends on a probabilistic formula instead of a random deployment; the other is that the heuristic factor is expressed by the extra picking time of each order instead of the total. At last, an actual simulation is made on an automated picking system with parallel dispensers. The simulation results proved the optimization value and the validity of improvement on MMAS.