The work aims to improve the static and dynamic structural performance of the silicon wafer robot and realize the lightweight structural design. The multi-objective optimization theory combined with the analytic hierarchy process was introduced to realize the structural optimization design of the robot's big arm. The load condition of big arm was analyzed in terms of the design scheme, the solid isotropic microstructures with penalization (SMIP) model was used to build the multi-objective optimization numerical model, and the optimization solution was done via optimality criteria. The analytic hierarchy process in the mathematical statistics was introduced to determine the weight ratio of sub-objective functions. The overall objective function about static stiffness and first-order natural frequency was constructed according to the compromise programming method. The optimization results analyzed that the compliance of the big arm reduced from 26.890 mm/N to 13.221 mm/N, the first-order natural frequency increased from 556.86 Hz to 629.90 Hz, and the structural mass decreased from 1.48 kg to 0.583 kg. The multi-objective optimization results show that, the improved design of the big arm of silicon wafer robot based on the multi-objective optimization theory not only improves the static stiffness effectively as the enhance of the first-order natural frequency indicates that the vibration suppression ability of the big arm is improved, but also realizes the lightweight design of the big arm. The introduction of analytic hierarchy process provides impersonal theoretical basis for the importance of sub-objective functions in multi-objective optimization problems.