Abstract: The bed and column are important assemblies of the grinder, and the characteristics of the joint surface directly affect the dynamic performance of the grinder. In order to explore the impact of the joint surface stiffness on the dynamic performance of the system, an equivalent spring finite element model of the joint surface stiffness is proposed for the joint surface of the grinder's bed and column. The accuracy of the model is verified by modal test, and the joint surfaces X, Y, and The influence of the stiffness in three directions of Z on the system mode. The simulation results show that: when the stiffness of the joint surface is change in a certain range of 2×10⁹~8×10⁹ N/m, The influence of Z-direction stiffness on the first to three modal frequencies of the system is the largest, and the influence on the first modal frequency is the largest, accounting for 90.2%; The X-direction stiffness of the joint surface mainly affects the second mode frequency of the system, accounting for 32%; The Y-direction stiffness of the joint surface mainly affects the third-order modal frequency of the system, accounting for 38%. It provides a new method to improve the dynamic characteristics of the whole machine and optimize the structure of the machine tool.