Abstract: A stack injection mold was designed according to characteristics of the balance ring of washing machine. The Moldflow software was used to simulate the filling, packing and warpage deformation processes of injectionmolded parts. Through the simulation of mold filling process, the number of gate and the size of runner were optimized, and the flow balance was achieved. The optimal control method and parameters of packing process were obtained by comparison of the results from the packing and warpage deformation processes with different packing parameters. The results indicated that the molding and assembling requirements for balance ring could be well met by the stack mold designed in this work.