The　geometric　errors　have　a　significant　effect　on　the　machining　accuracy　of　multi-axis　machine　tool.　Because　of　their　complex　inter-coupling,　the　process　to　control　these　geometric　errors　and　then　to　improve　the　machining　accuracy　on　this　basis　is　recognized　as　a　difficult　problem.　This　paper　proposes　a　method　based　on　the　product　of　exponential　(POE)　screw　theory　and　Morris　approach　for　volumetric　machining　accuracy　global　sensitivity　analysis　of　a　machine　tool.　When　a　five-axis　machine　tool　is　chosen　as　an　example,　there　are　five　screws　to　represent　the　six　basic　error　components　of　each　axis　(in　an　original　way)　according　to　the　geometric　definition　of　the　errors　and　screws.　This　type　of　POE　model　is　precise　and　succinct　enough　to　express　the　relation　of　each　of　the　components　as　the　Morris　method　is　based　on　the　elementary　effect　(EE).　The　method　can　compare　incidence　of　these　errors　and　be　used　to　describe　the　nonlinear　relationship　by　less　calculated　amount　in　a　global　system.　Based　on　the　POE　modelling,　the　Morris　method　is　adopted　to　identify　the　key　geometric　errors　which　have　a　greater　influence　on　the　machining　accuracy　by　global　sensitivity　analysis.　Finally,　according　to　the　results　obtained　from　analysis,　suggestions,　and　guidelines　are　provided　to　adjust　and　modify　the　machine　tool　components　to　improve　the　machining　accuracy　economically.