The error analysis of the RV reducer transmission is investigated,but the study on general method for the tolerance design of the RV reducer is less in present literature. A new method for the tolerance design of RV reducer- method of weighting is proposed. The mathematical model is established in the first step,the model is related to hysteretic errors and the input designed parameters. The method for determining the sensitivity and dimensions of the weight coefficient is introduced. The RV- 20 E type reducer is designed with this method,it is meet the design requirements both in theoretical analysis and trial tests. This method will have certain guiding significance for the tolerance design of RV reducer.