In　order　to　determine　the　key　factors　which　have　an　impact　on　the　machining　accuracy　of　a　machine　tool　after　its　machining　errors　occur,　a　new　method　analyzing　the　sensitivity　of　machine　tool　errors　based　on　the　theory　of　multi-body　system　kinematics　is　proposed.　Firstly,　the　method　assumes　a　machine　tool　to　be　several　rigid　bodies　according　to　the　theory　of　multi-body　system　kinematics,　establishes　the　body　reference　coordinate　system　and　the　kinematic　reference　coordinate　system　on　each　rigid　body,　and　constructs　the　constraint　equation　by　using　the　method　of　describing　the　center　of　the　tool　and　the　machining　point　in　the　system　coordinates　to　solve　the　machining　errors　of　the　machine　tool.　Then,　it　gives　the　sensitivities　of　error　parameters　by　taking　derivative　of　errors　and　establishes　the　impact　analysis　model.　The　calculation　and　analysis　for　an　example　show　that　when　using　the　method　the　key　factors　that　have　significant　influence　on　machine　tool　errors　can　be　identified　efficiently.　It　can　provide　the　theoretical　basis　for　designers　and　users　to　improve　machine　tools.