The constitutive model for titanium alloy was researched to describe the dynamic recovery (DRV) and dynamic recrystallization (DRX) behavior during hot deformation. During this process, based on the constructing method of classical plasticity and viscoplastic unified constitutive model using internal state variables, the constitutive model was developed considering the deformation mechanism of materials by deriving the correlative relations. The proposed model is able to offer more clearly physical insight. At last, the deformation behavior of a new kind of metastable β Ti2448 titanium alloy was described by the proposed model during hot deformation. The stress-strain curves predicted by the developed constitutive model well agree with experimental results, which confirms that the developed constitutive model can give an accurate estimate of the flow stress of Ti2448 titanium alloy. The developed model is effective, the method is reasonable and it can provide an effect method to model the flow behavior of metastable β titanium alloys during hot deformation.