Movable platen is key component of a plastic injection machine. In this paper the movable platen of HBT80X/1 plastic injection moulding machine is redesigned using topology optimization method. The SIMP method and OC method were applied as the optimization principle and Optimality Criteria. After given the topology structure, the refined structure is designed with experience. The results show that the weight and maximum placement of the new shape were 53Kg and 0.009mm less than the original design.