Camshaft grinding accuracy is mainly affected by the selfexcited vibration of the machine tool spindle system, forced vibration and thermal deformation, and modal analysis is the foundation of dynamic analysis. Therefore, it is necessary to analyze deeply the influence of spindle vibration on grinding precision. By taking JKM8 camshaft grinding machine head spindle system as the research object, the finite element model (FEM) of the rotorbearing system was established to carry out modal analysis by using the elastic supporting element to simulate hydrostatic bearing, obtained the first 6 order modal parameters of the system, and the law of natural frequency of the system changes along with the supporting stiffness was studied by using the parameter discussion method. The results prove that the spindle speed is far below the first critical speed, so it would not happen resonance. The bearing stiffness of the hydrostatic bearing has great influence on the low order natural frequency of the main shaft system, and the amplitude of natural frequency increase is significantly decreased when the stiffness of the hydrostatic bearing is greater than 300 N/μm. The research results provide a theoretical basis for the optimization of spindle system of grinding machine.