Isothermal　compression　testing　of　Ti-5.8Al-3Sn-5Zr-0.5Mo-1.0Nb-1.0Ta-0.4Si-0.2Er　titanium　alloy　is　performed　on　a　Gleeble-3500　thermal　simulator,　and　the　corresponding　microstructures　are　analyzed　to　clarify　the　softening　mechanism　and　participates　evolution.　A　constitutive　equation　compensated　by　strain　has　been　established　to　describe　the　hot　deformation　behavior　of　the　alloy.　The　deformation　activation　energies　are　calculated　to　be　369760.93-699310.86　J/mol　in　alpha+beta　two-phase　region　and　268030.03-325800.41　J/mol　in　beta　single-phase　region.　At　a　temperature　of　880　degrees　C,　the　main　softening　mechanism　is　the　continuous　dynamic　recrystallization　of　lamellar　a　colony,　controlled　by　the　mechanical　rotation　of　the　sub-grain　followed　by　dislocation　climbing　and　annihilation　by　diffusion.　Meanwhile,　the　dominant　softening　mechanism　is　the　discontinuous　dynamic　recrystallization　of　b　phase　during　the　deformation　at　temperatures　of　920　degrees　C-1080　degrees　C.　Silicide　containing　Er　with　an　average　diameter　of　20　nm　is　formed　during　the　water　quenching.