Abstract: The analysis of the sensitivity of the input parameters to the dynamic responses of the reactor system is an important prerequisite for optimal design. In this paper, the contact stiffness and clearance of the key parts of the reactor system are taken as input variables, and the Sobol’s method is used to analyze the sensitivity of the key input parameters to the dynamic response of the system under the seismic condition. The global sensitivity coefficient and the order of importance of the input parameters are obtained. The results were also tested using the K-S measure sensitivity analysis method. The analysis shows that the seismic response of the fuel assembly is sensitive to the change of the contact stiffness at two locations, and the tangential load extreme value is most sensitive to the change of the contact stiffness at the location. The relevant methods and analysis processes can be extended to the reactor coolant system and other main equipment to provide the method for quantitative analysis and data support for the selection of optimized design parameters.