Aiming at the problem that the working mode parameters of grinding vibration caused by poor robot rigidity are hard to predict, the relationship model between process parameters and the natural frequency of the system was established. Based on the simplified robot grinding system, the measurement method of grinding contact stiffness was proposed. The vibration matrix equation was solved by using perturbation method and the process parameters were linked with the working mode through grinding contact stiffness. The robot grinding platform of belt grinding machine was used for experimental verification, and the working modes were measured with different process parameters, the accuracy of the mathematical model was verified by compared the measured values with the calculated values, and the influence rules of different grinding process parameters on contact rigidity and system natural frequency were further obtained. The research results provide reference for the subsequent research on avoiding or suppressing the grinding vibration generated by the robotic belt grinding system as well as the optimization of grinding process parameters.