Abstract: Space rigid frame structures have a wide range of applications in architecture, transportation, aerospace, machinery, energy, and other fields. Reducing the dead weight of a space rigid frame structure can not only reduce the manufacturing cost, but also reduce the driving energy consumption of the system in specific application scenarios such as aircraft and vehicles. Under the given geometric shape and mechanical performance requirements, the topological form of a space rigid frame structure becomes the key design element to determine the overall weight of the structure. Considering the requirements of dynamic characteristics of a polyhedral rigid frame structure subjected to complex multi load cases, a lightweight design method including the comprehensive objective function of loading and natural frequencies is proposed. The compromise programming method is used to construct the objective function, the weight coefficient of each working condition and each order frequency is determined by the analytic hierarchy process, and the variable density method with penalty factors is used to optimize the topology of the structure. Compared with the optimization method using rigid constraint natural frequencies, the optimization result of the method proposed is more uniform, the weight of the optimized structure is reduced by 18.6% compared with the original design, and the displacement stress index of each working condition is significantly improved. The research results show that this lightweight design method is feasible and reliable.