According to the distribution type of the uncertain parameters not acquired accurately in the probabilistic reliability, the interval model was used to describe the uncertain parameters. Various calculation methods were used to research the non-probabilistic reliability responding to different condition between the stress interval and the resistance interval. The reliability index of the transmission shaft of a mechanical device was compared between probabilistic reliability and non-probabilistic reliability. And the corresponding changes of the non-probabilistic reliability index were observed with different deviation of the uncertain parameters, analysis of non-probabilistic index has shown that with the increasing uncertain level of the parameter, the non-probabilistic reliability of propeller shaft was gradually reducing. And uncertain level of the different design parameter had a distinct influence on reliability index.