Hot compression tests of as-cast TB6 titanium alloy were performed at the temperature of 800-1150°C and the strain rate range of 0.001-10s_^?1 to examine microstructure evolution associated with stress induced martensite (SIM). The results reveal the occurrence of the SIM with the dendritic morphology in present alloy during hot compression process. The orthorhombic structure of SIM was confirmed for the alloy. It was found that the SIM nucleates both in the β grain interior and at grain boundary. TheSalloy composition uniformity and internal stress are strongly dominated by strain rate and deformation temperature, which is responsible for the amounts of SIM. The content of SIM at different strain rate is related to the temperature ranges. More contents of SIM appear at the strain rate of 0.1s_^-1 for the temperature of 800℃~900℃, at 0.01s_^-1 and 1s_^-1 for the temperature of 900℃~1000℃, at the strain rate of 1s_^-1 for the temperature of above 1000℃. 50% martensite can be obtained at an optimal combination of the temperature of 925℃ and the strain rate range of 1s_^-1.