The purpose of this paper is to explore the influence degree of reliability to every basic random variable and provide a theoretical reference for the design of mechanical product. Therefore, based on the finite element method (FEM), the geared-rotor dynamic model which consists of parametric rigid disks and flexible shafts is established and analyzed. Combining the probabilistic perturb ation method and reliability design, the random response model and reliability model are established, and then based on the modified reliability-based sensitivity design method, the dynamic model of geared-rotor system is proposed. The influences of geared-rotor parameters on the reliability-based sensitivity of rotor system are discussed and studied thoroughly, the variables of mixed types are normalized and dimensionless, and then the influence degree of reliability to every basic random variable are obtained. As a result, it is seen that the meshing angle, which should be controlled strictly, has a greater influence degree on reliability of gear rotors.