The influences of thermal stabilization of austenitic on the onset temperature for a martensite transformation in T91 ferritic heat-resistant steel were studied by high-resolution differential dilatometer.The phase trans- formation kinetic information was obtained by adopting lever rule from the recorded dilatometric curves.The results show that an inverse stabilization,featured by the damage of“the atmosphere of carbon atoms”and the increase of the starting temperature for martensite transformation takes place when the T91 ferritic steel is isothermally treated above the M_s point,and it becomes strong with increasing the holding time.While the continued temperature for martensite transformation decreases gradually when isothermally holding at a temperature below M_s point.The observed inverse stabilization behavior could be attributed to the relatively high temperature of M_s point in the explored T91 ferritic heat-resistant steel. The influences of thermal stabilization of austenitic on the onset temperature for a martensite transformation in T91 ferritic heat-resistant steel were studied by high-resolution differential dilatometer. The phase trans-formation kinetic information was obtained by incorporating lever rule from the recorded dilatometric curves. The results show that an inverse stabilization, featured by the damage of “the atmosphere of carbon atoms ” and the increase of the starting temperature for martensite transformation takes place when the T91 ferritic steel is isothermally treated above the M_s point, and it becomes strong with increasing the holding time. Whilst the continued temperature for martensite transformation shonsteen when isothermally holding at a temperature below M_s point. observed inverse stabilization behavior could be attributed relatively to temperature of M_s point in the explored T91 ferritic heat-resistant steel.