To　improve　the　machining　accuracy　of　five-axis　NC　machine　tools,　this　paper　analyzes　the　RTCP　errors　of　five-axis　machine　tools　with　dual　head.　The　error　analysis　model　is　established　based　on　the　basic　theory　of　a　multi-body　system　and　six-degrees　of　freedom　of　the　rigid　body.　RTCP　errors　of　tool　center　point　and　tool　vector　are　deeply　analyzed.　The　error　formulas　of　tool　center　point　and　tool　vector　are　deduced.　By　comparing　the　ideal　and　actual　cutter　path　that　are　generated　by　tool　path　simulation　software,　the　model　is　demonstrated　to　be　correct.　The　study　provides　fundamental　theory　for　error　compensation　and　error　analysis.