Considering the influence of random factors, using the HL-RF method to calculate the reliability, the reliability optimization design of the gearbox is studied. The reliability optimization design of the gearbox is studied by using the importance sampling. This paper puts forward the method of reliability fuzzy optimum design, which is the deepening of reliability, optimum design, and fuzzy optimum design. Under the influence of fuzziness, a multi-objective reliability fuzzy optimization model of the gearbox is established. By using the multi-objective fuzzy optimization method, the reliability fuzzy optimization design of the gearbox is carried out.