Tie bars are key components of a plastic injection machine. They very easily fatigue in periodically long term operations due to the bending moment transferred to them by the bending of the stationary platen. This problem can be easily overcome by reducing the deflection of the stationary platen through topology optimization of the platen structure by applying a cost or weight constraint. In this paper, the self-organization method was introduced to optimize the topology of the stationary platen. Topology design optimizes material allocation, i.e. strengthening locations of high loads and minimizing material usage at other locations. By applying this method to the stationary platen design, the deflection of the platen could be reduced, which correspondingly reduces the bending load of the tie bars and thus extending their operating life.