The　performance　of　the　milling　head　is　affected　by　the　machining　and　assembly　process　of　the　parts.　The　key　to　improving　machining　accuracy　and　reliability　of　swing　angle　milling　head　is　to　establish　the　precision　prediction　model.　Therefore,　a　precision　prediction　model　of　swing　angle　milling　head　under　the　influence　of　multiple　errors＇　sources　is　built.　The　transmission　and　accumulation　of　machining　and　assembly　errors　along　the　assembly　sequence　path　for　the　transmission　system　are　carried　out.　All　essential　components　on　the　assembly　sequence　path　are　considered.　In　addition,　the　secondary　impact　of　the　bearing　seat　hole　is　also　taken　into　account.　The　source　of　the　gear　assembly　errors　is　explained.　The　predicted　range　of　transmission　error　based　on　the　coupling　relationship　between　assembly　errors　and　transmission　error　is　obtained.　A　precision　experiment　is　carried　out,　and　the　result　is　within　the　predicted　range.　This　research　demonstrates　that　the　errors＇　coupling　relationship　considered　in　this　paper　does　exist　and　has　an　effect　on　transmission　error,　which　provides　a　new　idea　for　calculating　transmission　error　of　other　gear　systems.