This　article　introduced　the　current　research　progress　and　theoretical　basis　of　designing　the　twin　induced　plasticity　(TWIP)/transformation　induced　plasticity　(TRIP)　metastable　β　titanium　alloys,　and　summarized　β-grain　sizes,　yield　strength　and　work　hardening　capability　of　the　double　twined　{332}　and　{112}　metastable　β　titanium　alloys.　The　application　and　limitation　of　combination　times　(Bo)-d　electron　orbit　energy　level　(Md)　diagram　in　the　design　of　multi-component　titanium　alloys　were　further　discussed,　especially　the　effect　of　different　secondary　phases　(α-phase　and　ω-phase)　on　the　stability　of　the　matrix　β-phase.　The　factors　that　influence　the　deformation　mechanisms　of　TWIP/TRIP　metastable　β　titanium　alloys　are　emphasized　in　terms　of　the　matrix　β　phase　stability,　precipitated　phases,　β-grain　sizes　and　crystallographic　orientations.　And　the　current　deficiencies　of　this　field　were　analyzed.　Furthermore,　the　effect　of　double　twinning　mechanisms　on　the　mechanical　properties　of　titanium　alloys　was　briefly　discussed　as　well.　Finally,　by　summarizing　the　research　progress　and　related　issues,　this　article　conveyed　the　new　insights　for　the　development　of　high-strength　and　tough　titanium　alloys.　©　2021,　Science　Press.　All　right　reserved.