T122 steel has been used to produce superheater or reheater of ultra supercritical boilers. With the help of chemical phase extraction and microstructure characterization, the performance of aging precipitates of T122 steel, such as M23C6 carbide, Laves phase and MX phase was investigated, the strengthening mechanism of the steel was discussed, and the thermal yield stress of lath substructure, dislocations and precipitates of the steel were calculated. It was found that lath substructure and dislocations dominated the strengthening attribution and precipitation hardening went second to the strengthening attribution. T122 steel has been used to produce superheater or reheater of ultra supercritical boilers. With the help of chemical phase extraction and microstructure characterization, the performance of aging precipitates of T122 steel, such as M23C6 carbide, Laves phase and MX phase was investigated, strengthening mechanism of the steel was discussed, and the thermal yield stress of lath substructure, dislocations and precipitates of the steel were calculated. It was found that lath substructure and dislocations dominated the strengthening attribution and precipitation hardening went second to the strengthening of steel attribution.