This　paper　based　on　the　self-designed　electro　spindle　bearing　system　test　bench　as　the　study　object.　By　calculating　angular　contact　ball　rolling　bearings　stiffness　under　different　preload,　and　fully　consider　the　joint　of　spindle　bearing　that　often　ignored　in　the　traditional　calculation.　After　getting　the　support　stiffness　of　the　bearing　and　joint,　build　dynamics　modeling　and　simulation　analysis　in　ANSYS,　with　MATRIX27　element　to　simulate　the　bearing　joint　support,　with　Beam189　unit　modeling　the　spindle.　Discusses　different　bearing　preload　about　spindle　system　modal,　compared　with　no　account　of　the　joint　stiffness　analysis,　highlight　the　necessity　of　the　joint　stiffness,　provide　a　useful　reference　for　the　study　of　dynamics　of　the　spindle　system.