Abstract: The existing flow stress models were analyzed.Aiming at the characteristics of flow stress of BT20 titanium alloy,a mathematical model has been put forward to determine flow stress under hot working condition.The propounded model can describe the flow stresses involved in the work hardening and work softening processes due to dynamic recrystallization and recovery,as well as the effect of temperature and strain rate.The models between peak strain,peak stress,steady state stress and deformation parameters have been also established,respectively.The preciseness of calculated results using these models is good to compare with the experimental results.