A 2PRU&1PRS-XY hybrid robot was proposed for the design requirements of robotic machining equipment for complex structural components. In order to apply the new hybrid robot to high-performance 5-axis machining, it is necessary to realize the dimensional design that takes into account the balanced optimization of multi kinematics performance. Therefore, in addition to analyzing the working space, motion/force transmission and dexterity indicators of hybrid robot, the difference index of transfer stability and accuracy was also proposed, and a scale design method based on the idea of multi-objective equilibrium optimization was designed. This method adopted standardized method to simplify the multi-parameter design space, applied response surface methodology to improve the efficiency of solving complex functional functions, and the optimization solution efficiency was improved by the principal component analysis method. Combined with subjective and objective combinatorial empowerment method and TOPSIS-based Pareto frontier method, multi-index comprehensive performance scoring was carried out. Using the proposed method, four dimensional parameter design schemes were obtained that balanced optimization efficiency and multi-objective equilibrium optimization. The optimization design of the main dimensional parameters of the hybrid robot was achieved, providing designers with multi-objective equilibrium decision-making references with different engineering design preferences.