A　novel　multi-output　porthole　extrusion　die　for　thin-walled　aluminum　alloy　profile　is　introduced　and　its　thermo-mechanical　modeling　for　the　analyses　of　metal　flow　and　elasto-plastic　deformation　is　developed.　In　order　to　explore　the　sources　of　undesirable　deformations,　two　key　deformation　behaviors　(non-uniform　relative　exit　velocity　of　profile　and　mandrel　deflection　of　extrusion　die)　which　play　considerable　effects　on　the　metal　flow　balance　are　analyzed　based　on　the　developed　numerical　model.　Finally,　the　optimization　design　of　the　multi-output　porthole　extrusion　die　structure　is　performed　for　the　improvement　of　extruded　profile　quality.　(C)　2018　The　Authors.　Published　by　Elsevier　B.V.