In order to accurately obtain the plastic processing deformation characteristics and thermal processing conditions of TC21 titanium alloy, and reasonably design the forging process parameters, the Gleeble-3500 thermal simulator was used to conduct isothermal thermal compression tests with constant strain rate, and the deformation temperatures of TC21 titanium alloy was 830-1010 ℃, the thermal deformation behavior under the condition of strain rates of 0.01-10 s-1 was studied, the constitutive equation of TC21 titanium alloy was derived by using the Arrhenius hyperbolic sine function. Based on the dynamic materials model(DMM), the thermal processing map of TC21 titanium alloy was established. The results show that under the deformation conditions of this test, the flow stress of alloy increases with the decreasing of deformation temperature and the increasing of strain rate. According to the thermal processing map, the thermal processing safety zone of alloy is determined as: the deformation temperature of 900-940 ℃, the strain rate of 0.01-0.05 s-1 and the deformation temperature of 970-1010 ℃, the strain rate of 0.01-0.08 s-1.