Abstract: When a turboshaft engine was test running for 656.4 h in the factory, a gas turbine blade broke at the extended root section of the tenon. The crack distribution, macroscopic and microscopic morphology of the fracture and stress state of cracking part of the blades were studied, and the fracture reason of the blade was analyzed. The results show that the failure property of the blade was fatigue, and the fatigue crack was originated from the inner surface of the first cooling chamber inside the exhaust side of the extended root section of the tenon. Stress concentration was not considered in design of this type of blade tenon cooling structure, and the cooling channel had a large turning angle, resulting in a high stress level, and eventually leading to fracture and cracking of the blades.