In order to improve performance of 4-UPS-RPS high-speed spatial parallel robot, the elastic dynamics optimization design was executed. The influence law of the mass of moving platform and the diameter of driving limbs on the dynamic performance, which includes kinematics output response and maximum dynamic stress of driving limbs, were discussed. On these grounds, the mass of moving platform and the diameter of driving limbs were optimized. The simulation results show obvious improvement of the dynamics performance for 4-UPS-RPS parallel robot, therefore the theoretical basis are provided.