The part tolerance design of RV reducer is a major difficulty in its research and development process. A method based on fuzzy analytic hierarchy process is proposed for tolerance design of RV reducer. The sensitivity weight coefficient of part parameter error to hysteresis degree is constructed by sensitivity analysis, and the weight coefficient of part processing difficulty is constructed by triangular fuzzy-analysis hierarchy process. Based on the geometric mean method, the weight expression of the part design parameter is established to calculate the hysteresis of the RV reducer, so as to realize the tolerance assignment of the part design parameters. The theory and experimental results show that the method is feasible and has guiding significance for RV reducer tolerance design.