Abstract: The second last blades of low-pressure rotor in a thermal power plant fractured during service. The fracture reasons of the blades were analyzed by means of macroscopic examination, chemical composition analysis, EDS and SEM analysis, metallographic examination and mechanical property test. The results show that there were a lot of defects in the inlet side blade surface electric spark strengthened layer, and cracks initiated from the stress concentrated inlet side leading edge position under the severe operating mode. The low impact toughness and high notch sensitivity and embrittlement tendency of the blade base material promoted the crack propagation from the strengthened layer to the substrate. And the steam flow impact and other stresses action accelerated the growth of the cracks during operation, which led to the fatigue fracture of the blades.