Abstract: Low pressure penultimate blades of a turbine set cracked during running, and the cracking reason was analyzed by means of chemical compositions analysis, mechanical properties testing, metallographic examination and so on. The results show that the cracking initiated at the stress concentration position on the maximum stress surface of blade root. Existing closed angle and notch at the blade shape conductor transition region was the main reason for the cracking, and inclusions near the surface also had a certain impact on the cracking