The invention discloses a system for testing the dynamic stiffness property of a spindle rotor. The system comprises a spindle damping and clamping test bench, wherein the lower part of the spindle damping and clamping test bench is connected with a damping device; the upper part of the spindle damping and clamping test bench is connected with a movable spindle clamping device; the spindle rotor clamped by the movable spindle clamping device is sleeved with a load transfer device in interference fit; the load transfer device is connected with an eddy current displacement sensor; the spindle damping and clamping test bench is provided with a loading air cylinder in a vertical installation manner; the front end of the loading air cylinder is connected with a force sensor; the top end of a output shaft of the loading air cylinder is matched with the load transfer device through a force applying tip; signal output ends of the eddy current displacement sensor and the force sensor are connected through a signal conditioning module, a four-channel data collection card and a central control bench. Testing of radial dynamic stiffness of a spindle is achieved, the problem of dynamic loading of the spindle and the problem of dynamic deformation pickup can be effectively solved and the designing and processing level of the spindle is improved.