Abstract: Based on the stochastic perturbation and fourth moment techniques, the theory of reliability design is combined with sensitivity analysis to develop a mathematical model for reliability-based sensitivity of mechanical components. Such a reliability-based sensitivity depending on the incomplete information on probability is extensively discussed, and a numerical method for the reliability-based sensitivity design is correspondingly presented, with a mathematical evaluation method given in which the reliability of mechanical components changes with design parameters. Furthermore, how the reliability-based sensitivity changes and the effect of design parameters on the reliability of mechanical components are studied with ideal numerical design results obtained. The method proposed thus provides the reliability design of mechanical components with a theoretical reference.