The problem of randomness and fuzziness of mechanical design could effectively dealed with through the fuzzy reliability optimization design which established by the combination of fuzzy mathematics method and mechanical optimization technique.Taking the multi-stage planetary gear train as research object,the optimization and allocation of transmission ratio is implemented by the conventional optimization design method.On this basis,taking the fuzzy reliability constraints as the main constraint condition,the volume,transmission efficiency and contact ratio as object,the multi-objective fuzzy reliability optimization mathematical model is established.Then the fuzzy reliability optimization design is transformed into conventional reliability optimization design through the multistage fuzzy comprehensive evaluation,and the optimization design is carried out by using Matlab optimization toolbox.