Traditional planetary cutter mechanism design needs repeated trial and verification to determine a design scheme that meets the given conditions, and the scheme is generally not the best; The conventional single objective optimization design usually only aims at a certain requirement to achieve a certain optimal performance, neglecting the optimal comprehensive performance of the product. In order to solve the above problems, the reliability theory and optimization design technology are applied, and the compact structure, transmission efficiency, transmission stability and bearing capacity of the planetary cutter mechanism are comprehensively considered. Taking the minimum volume, maximum efficiency and maximum coincidence degree of the mechanism as the objective function, a multi-objective optimization design mathematical model different from the existing models is established by using the safety factor method and other constraints, Matlab software is used for optimization calculation. The results show that compared with the conventional design, the volume of the multi-objective optimization design is reduced by 79.97% and the coincidence degree is increased by 2.64% under the premise of almost constant transmission efficiency; Compared with the conventional single objective optimization design, although the single index is not optimal, the indexes are more balanced and the optimization effect is obvious.