Abstract: In order to study the microstructure transformation,Laves precipitate behavior and its influence on the strength of T92 steel during service,creep tests were performed at 649℃ with different stress levels.Then use optical microscopy,scanning-electron microscopy and transmission electron microscopy to observe the microstructure and precipitates transformation.the hardness variation was tested.The results show that the microstructure of T92 steel after heat treatment was martensite with dense dislocation and many precipitations including M23C6 and MX precipated in the steel.Laves phase appeared after creep,which precipated as the ways consisted of attaching on M23C6 and along the grain boundaries alone.The rate of ripening of Laves phase was rapider than M23C6.The Vickers hardness decreased during creep with the prolongation of the time,which was resulted as precipitation of Laves phase in the steel.