Abstract: Considering the uncertain influencing factors on the worm-gear pair as the main transmission mechanism of traction machines, the reliability modes were developed on the basis of its failure modes. The reliability and its sensitivity of the worm-gear pair were analyzed to determine the impacts of mutative random variables on the reliability. Then, the design of the pair was optimized to improve the main transmission mechanism with an appropriate reliability index. Introducing the reliability sensitivity into the model of optimization design, the robust reliability design can be attributed to the problem of multiobjective optimization to satisfy the requirements for reliability. A numerical example was given to verify the practicality and effectiveness of the method proposed.