The　heavy　load　angularly　defecting　milling　head　is　an　important　functional　component　of　5-axis　CNC　machine　tool,　which　is　used　for　large　and　complex　parts　with　free-form　surface　processing.　The　paper　constructs　the　architecture　of　key　technology　for　heavy　load　angularly　defecting　milling　head　based　on　demand　of　independently　developing　of　milling　head.　The　architecture　includes　theory　investigation　and　experiment　analysis.　Theory　investigation　is　the　base　of　the　architecture,　which　includes　kinematics　analysis,　static　analysis,　dynamics　analysis,　thermal　characteristic　analysis　and　thermo-mechanical　coupling　analysis.　Experiment　analysis　verifies　the　theory　investigation,　which　mainly　includes　modal　testing,　thermal　characteristic　experiment　and　precision　experiment.　The　paper　focuses　on　elucidating　the　architecture　of　all　key　technology　of　milling　head,　the　following　papers　will　discuss　the　detail　of　the　key　technology　respectively　in　the　architecture.　The　study　will　provide　academic　and　technical　support　for　milling　head　design.