In order to improve the design reliability of a retracting actuator, the reliability was analyzed and obtained by NESSUS (Numerical Evaluation of Stochastic Structures Under Stress) software based on the stress-strength interference theory, and the sensitivity and importance analysis on random variables which affect the design reliability were also done. Results show that the design reliability of the acuator is 0.99999999986, and the relative error between the test value is 1.3E-10, which is acceptable in engineering. The parameters that have relatively greater effect on the reliability orderes in degree as following diameter of shear pin, active area of output pressure, gunpowder impetus and density of detonator output charge. The consistency of these parameters should be guaranteed in material selection and product processing.