High　speed　motorized　spindle　has　become　a　key　functional　unit　of　high　speed　machine　tools　and　effectively　promotes　the　development　of　machine　tool　technology.　The　development　of　higher　speed　and　more　power　puts　forward　the　stricter　requirement　for　the　performance　of　motorized　spindle,　especially　the　dynamic　performance　which　affects　the　machining　accuracy,　reliability,　and　production　efficiency.　To　overcome　the　problems　of　ineffective　loading　and　dynamic　performance　measurement　of　motorized　spindle,　a　noncontact　electromagnetic　loading　device　is　developed.　The　cutting　load　can　be　simulated　by　using　electromagnetic　force.　A　new　method　of　measuring　force　by　force　sensors　is　presented,　and　the　steady　and　transient　loading　force　could　be　measured　exactly.　After　the　high　speed　machine　spindle　is　tested,　the　frequency　response　curves　of　the　spindle　relative　to　machine　table　are　collected　at　0　similar　to　12000　rpm;　then　the　relationships　between　stiffness　and　speeds　as　well　as　between　damping　ratio　and　speeds　are　obtained.　The　result　shows　that　not　only　the　static　and　dynamic　stiffness　but　also　the　damping　ratio　declined　with　the　increase　of　speed.