In order to improve the riveting precision, the finite element method and topological optimization design based on the variable density method were employed to design the pedestal of horizontal rocket rivet fixture. Topological optimization model was set up based on static analysis of the original designed pedestal under various typical load cases. Topological optimization results of various load cases were compared with original pedestal. The result showed deficiencies of the original pedestal, and a new model was built based on topological optimization results. The analysis of topological model was carried out by applying the finite element method. The results show that the stiffness of pedestal was remarkably improved; the stress distribution was more homogenized and the displacement of the guide rail was decreased after optimization. This method could also provide reference and guidance for designing other complicated structures.