The　transmission　network　is　generally　considered　as　three-phase　balanced,　while　the　consideration　of　threephase　unbalance　is　mainly　on　distribution　networks.　However,　with　the　increasingly　interconnection　of　renewable　energy,　such　as　wind　energy,　onto　transmission　networks,　non-adoption　of　commutation　long　transmission　lines　usually　results　in　unbalanced　line　parameters.　Therefore,　developing　reliable　three-phase　power　flow　algorithms　for　transmission　and　distribution　(T&D)　systems　becomes　more　and　more　important　for　the　reliable　and　safe　operation　of　emerging　power　systems.　Among　the　many　three-phase　power　flow　algorithms,　Newton　Raphson　method　(NRM)　and　its　variants　occupy　a　large　share,　due　to　their　ability　in　dealing　with　multiple　sources　and　looped　sub-networks.　However,　they　are　sensitive　to　the　initial　value,　and　can　hardly　ensure　convergence　to　a　physically　meaningful　solution　with　improper　initial　values,　especially　for　three-phase　unbalanced　system.　To　this　end,　a　general　three-phase　power　flow　method　for　T&D　systems　is　proposed　based　on　the　holomorphic　embedding　method　(HEM),　and　the　advantages　of　the　proposed　method　compared　with　traditional　NRM　in　solving　the　power　flow　problem　to　a　physically　meaningful　solution　are　theoretically　analyzed.　Based　on　the　IEEE　33　system,　the　modified　IEEE　123　system,　and　a　regional　power　grid　in　China,　it　is　verified　that　the　proposed　method　has　the　advantages　of　high　computational　efficiency,　reliable　converging　ability,　and　independence　to　the　initial　value.