Abstract: By thermal simulation, the HAZ microstructures of ASTMA213-T92 steel was studied. The results show that when the peak temperature (T_max) of simulated thermal cycle is lower than A_C1 of T92, the structure in HAZ is tempered martensite. When T_max is above A_C1, M-A appears in HAZ,which is distributed mainly in martensite lath boundary, austensite grain boundary and inside of transforming martensite lath. M-A size is much larger in coarse grain zone with the T_max of 1350℃. The microstructures at the T_max of 740- 815,870,970,1350℃ can present typical characteristics of different zones in HAZ respectively.