Parts　of　geometric　error　coupled　into　space　error　is　the　main　reason　that　affects　machining　accuracy　of　machine　tools;　therefore,　how　to　determine　the　effect　of　geometric　error　to　the　machining　accuracy　and　then　assigning　geometry　precision　of　parts　economically　is　a　difficult　problem　in　machine　tool　designing　process.　Therefore,　based　on　multi-body　system　theory,　a　sensitivity　analysis　method　of　geometric　error　is　put　forward　in　this　paper.　Let＇s　take　precision　vertical　machining　center　for　an　example.　Firstly,　an　accuracy　model　of　machining　center　is　established　based　on　multi-body　system　theory,　and　with　21　geometric　errors　obtained　through　experimental　verification,　key　error　sources　affecting　the　machining　accuracy　are　finally　identified　by　sensitivity　analysis.　The　example　analysis　shows　that　the　proposed　method　can　effectively　identify　the　main　geometric　errors　of　parts　that　have　great　influence　on　volumetric　error　of　machine　tool,　and　thus　provides　important　theoretical　basis　to　improve　the　accuracy　of　machine　tool　economically.