The work aims to optimize the structure of a stack-manipulator for packaging with Ansys Workbench, so as to reduce the structure weight and improve working efficiency and positioning accuracy of the manipulator. Modeling of the manipulator was done and the static and modal analyses were carried out with stress analysis software. The key structural parts of the manipulator were topologically optimized through the variable density method of topology optimization. Under the condition of satisfying the overall strength of the manipulator, its qualitative distribution was changed and a reasonable driving motor was selected in order to realize less vibration and light weight of the manipulator. In conclusion, the variable density method of topology optimization is an effective and feasible way for structural optimization of the manipulator and improving its work efficiency.