The multi-stage gearboxes for obtaining a large driving force are used for various purposes in industry, and helical gear reducer which is easy to manufacture and repair is generally used. Since industrial gearboxes are used in different operating conditions and in harsh environments, they are designed with a relatively high safety factor. Therefore, it is difficult to confirm the life of the gearbox because of its durability. In this paper, accelerated life tests are carried out with the torque that affects the life of small helical gearbox, and the results are statistically analyzed to confirm the reliability factors such as the life of the gearbox, the shape parameters and the acceleration index using statistical methods.