The spindle is the core part of the high speed milling machine, its dynamic characteristics directly affect the machining accuracy of the milling machine.Taking a German GMN high⁃speed milling machine electric spindle as an example, the finite element method was used to establish a finite element model of the spindle⁃bearing system, the natural vibration characteristics of the spindle were studied, and the influence of bearing stiffness on the natural vibration mode and critical speed of the spindle was analyzed.On this basis, the unbalanced response characteristics of the high⁃speed spindle were studied, and the influence of the unbalance amount and position on the vibration sensitivity of the spindle was analyzed. It was found that the unbalanced response at both ends of the spindle was sensitive, especially at the end where the tool was connected. The results could provide a certain reference for the dynamic design of the high⁃speed machine tool spindle system.