The　fatigue　properties　of　TC21　Ti-alloy　for　thin-wall　tube　specimen　are　investigated　under　uniaxial,　tension-torsion　proportional,　non-proportional　and　variable　amplitude　loading.　All　tests　are　strain-controlled.　The　results　indicate　that　cyclic　softening　behavior　is　shown　for　TC21　alloy　under　uniaxial　and　proportional　tension-torsion　constant　amplitude　loading,　and　the　cyclic　softening　is　more　obvious　under　large　strain　amplitude　loading.　The　large　strain　loading　followed　by　small　strain　loading　under　non-proportional　loading,　shows　that　the　cyclic　hardening　for　tension　stress　is　responded　in　the　smaller　strain　loading　stage　due　to　the　previous　larger　strain　loading　strengthening　for　tensional　properties.