Abstract: The microstructure change of T92 steel made in China during endurance testing process was investigated at the temperature of 620, 650, 700 ℃ with different stress. The results show that the martensite laths microstructure morphology of the steel had not been changed during endurance testing process at 620, 650 ℃, the number and size of the main precipitates in the steel increased with the increase of the endurance testing time, and micropores appeared at the grain boundary when the time to a certain value. The number and size of the precipitates increased severely at 700 ℃, and the martensite laths microstructure morphology of the steel disappeared.