Strain　rate　sensitivity　will　change　the　cyclic　mechanical　response　of　materials　under　multiaxial　thermomechanical　fatigue　loading;　thus,　it　will　lead　to　errors　in　fatigue　life　prediction　if　strain　rate　sensitivity　is　not　considered　in　constitutive　simulation.　In　order　to　more　accurately　express　the　time/rate　dependence　of　viscoplastic　behavior,　a　strain　rate　sensitivity　factor　is　proposed　to　modify　the　viscoplastic　function　of　Chaboche　model　first.　On　this　basis,　a　viscoplastic　constitutive　model　considering　strain　rate　sensitivity　under　multiaxial　thermomechanical　fatigue　loading　is　proposed,　which　can　describe　the　varying　influence　of　strain　rate　sensitivity　on　cyclic　mechanical　behavior.　Meanwhile,　the　exponential　isotropic　hardening　rule　with　the　linear　term　is　adopted　to　characterize　the　initial　rapid　softening　and　subsequent　stable　softening　of　the　material　under　fatigue　loading　at　elevated　temperature.　Moreover,　the　material-dependent　nonproportional　hardening　coefficient　and　the　loading　path-dependent　rotation　factor　are　used　in　the　kinematic　hardening　rule　to　consider　the　effect　of　nonproportional　additional　hardening　on　the　cyclic　mechanical　behavior　of　materials.　Finally,　the　proposed　method　is　verified　by　the　stress-strain　data　of　titanium　alloy　TC4　and　Ni-based　superalloy　GH4169　under　uniaxial　and　multiaxial　thermomechanical　fatigue　loadings,　and　a　good　agreement　is　obtained.