Abstract: the optimization of fixed platen structure of injection molding machine was carried out using criteria method, and the SIMP model was solved based on variable density method. the ribs were distributed properly according to the optimal design of structure to obtain better material configuration.With satisfaction of the technical indexes, the deformation of the fixed platen decreased by 3. 5%，the weight decreased by 9. 5%，and stiffness was improved. It was concluded that the optimization model of fixed platen was suitable for engineering application

Key words: topological optimization, variable density method, microstructure model, optimization criteria method, injection molding machine, platen