The　geometrical　error　of　rotation　axis　is　a　fundamental　error　source　for　five-axis　machine　tool　(FAMT).　Therefore,　enhancing　the　accuracy　of　rotation　axis　is　one　of　the　important　means　to　enhance　the　machining　accuracy　of　FAMT.　This　paper　developed　a　novel　approach　for　geometric　error　identification　of　rotation　axis.　Firstly,　a　single　axis　rotation　identification　model　using　double　ball　bar　is　established　based　on　Homogeneous　Transformation　Matrix　(HTM)　theory.　Secondly,　the　five　measurement　trajectories　are　developed　to　determine　the　geometric　errors　of　the　C-axis.　In　addition,　the　fourth-order　truncated　Fourier　series　is　used　to　fit　the　discrete　measurement　data　under　the　premise　of　considering　the　installation　error　of　the　double　ball　bar　instrument.　Finally,　simulation　and　experiments　indicate　that　the　proposed　method　is　effective　and　feasible.　The　SSE　values　of　the　fitting　model　are　above　90.39.　In　the　compensation　experiment　based　on　identification　method,　the　average　machining　accuracy　of　workpiece　has　been　improved　by　28.6%　compared　with　RTCP.