A physical model of microstructure evolution including dislocation density rate and grain growth rate was established based on the deformation mechanism for the hot forming of a class of two-phase titanium alloys. Further,a set of mechanism-based constitu-tive equations were proposed,in which the microstructure variables such as grain size and dislocation density were taken as internal state variables for characterizing the current material state. In the set of constitutive equations,the contributions of different mecha-nisms and individual phase to the deformation behavior were analyzed. The present equations have been applied to describe a correla-tion of the flow stress with the microstructure evolution of the TC6 alloy in hot forming. A physical model of microstructure evolution including dislocation density rate and grain growth rate was established based on the deformation mechanism for the hot forming of a class of two-phase titanium alloys. Further, a set of mechanism-based constitutive equations were proposed, in the the microstructure variables such as grain size and dislocation density were taken as internal state variables for characterizing the current material state. In the set of constitutive equations, the contributions of different mecha-nisms and individual phase to the deformation behavior were analyzed. The present equations have been applied to describe a correla tion of the flow stress with the microstructure evolution of the TC6 alloy in hot forming.