The　improvement　of　the　accuracy　grade　of　main　components　in　the　production　process　through　balancing　between　function　and　cost　helps　to　improve　the　overall　accuracy　of　machine　tools.　Therefore,　this　paper　presents　an　improved　value　analysis　method　and　uses　the　method　of　global　sensitivity　analysis　and　geometric　error　correlation　analysis　to　analyze　and　optimize　the　error　parameters　of　a　4-axis　machining　tool　based　on　the　proposed　method.　The　geometric　error　modeling　of　the　4-axis　machine　tool　was　established　by　using　the　homogeneous　transformation　matrices　(HTMs).　By　using　global　sensitivity　analysis,　the　degree　of　influence　of　each　error　parameter　on　the　accuracy　of　machine　tool　was　obtained,　and　functional　coefficient　and　cost　coefficient　of　value　analysis　were　gained　by　correlation　analysis.　An　optimization　model　for　geometric　error　budget　of　machine　tool　was　established　according　to　the　improved　value　analysis　theory,　and　the　machining　accuracy　of　machine　tool　was　optimized　according　to　the　improved　value　analysis　method.