Microstructure and mechanical properties of Ti600 high-temperature after thermal exposure at 600 ℃ for different times were studied. The results show that there is only a little precipitation during thermal exposure, which are mainly silicides and a2 phases. During thermal exposure, the deterioration of plasticity for Ti600 alloy is mainly due to the precipitations of silicides and a2 phases, and in them, the formation of a2 phase play main role. For Ti600 high-temperature titanium alloy, the main decrease stage of plasticity is resulting from the coarsening of a2 phase during thermal exposure process.