Gradient　microstructure　design　has　been　found　to　be　an　effective　approach　to　significantly　produce　the　utmost　advanced　structural　metallic　materials,　which　have　a　signature　in　mechanical　characteristic　of　strength-ductility-hardenability　combination.　In　this　work,　a　physical　theory　and　mechanism-based　numerical　model　are　developed　for　sophisticatedly　designing　the　gradient　microstructured　metals.　It　considers　the　gradient　distribution　of　grain　size,　twin,　martensite　and　austenite　in　a　metallic　alloy.　The　numerical　results　are　validated　through　experiments.　The　mechanical　performance　of　high　strength,　large　ductility　and　considerable　hardenability　is　achieved　and　their　trade-off　is　successfully　overcome.　(C)　2020　Acta　Materialia　Inc.　Published　by　Elsevier　Ltd.　All　rights　reserved.