The isothermal compression tests for air-cooled titanium alloy TC11 were carried out in the temperature range of 750~1100 ℃ and strain rate range of 0.001~10.0 s-1, and the high temperature flow behavior, the flow instability and the deformation mechanism were investigated inphase field andphase field for this alloy by using flow stress-strain curve and processing map. The results show that in excess of peak stress the flow stress decreases continuously with increasing of strain at low temperatures inphase, but first decreases and then reaches an approximately constant value at moderate and high temperatures inphase; the flow stress decreases slightly and then tends gradually toward a constant value with increasing of stain inphase field. In the processing maps of this alloy, the domains with high value of in phase are about (750~900 ℃, 0.001~0.006 s-1) and (900~1000 ℃, 0.001~0.02 s-1). In these two domains, the spheroidization oflamellae occurs, and the combination of spheroidization of lamellae andphase transformation happens, respectively. The domain with high value of inphase field is about (1000~1100 ℃, 0.003~0.3 s-1), where dynamic recrystallization undergoes. The above domains are desirably to be selected for hot working. The domains of flow instability are (750~875 ℃, 0.006~10.0 s-1), (875~975 ℃, 0.03~10.0 s-1) and (975~1100 ℃, 1.0~10.0 s-1), and the manifestations of flow instability are macroscopic shear, adiabatic shear band and non-uniform deformation of grains.