Abstract: A blade is fractured from the tenon, and according to the requirements, the fracture analysis, material inspection and trace analysis of the No. 16 blade and its corresponding tenon groove are carried out, and the results show that (1) The fracture nature of the No. 16 fourth-stage rotor blade is high-cycle fatigue, and there are multiple fatigue zones. The main fatigue source is located at the edge of the matching surface of the tenon and tenon, about 2.5mm away from the rear surface of the snap ring groove and about 4.9mm away from the bottom surface of the tenon, which is a short-line source. The initiation of fatigue cracks is related to the fretting damage of the side of the tenon. (2) The silver layer near the edge of the matching surface of the blade tenon and tenon groove is incomplete, there are sand residues on the surface of the metal matrix, and the tenon and tenon groove fit tightly, all these factors will deteriorate the surface contact state and cause local fretting damage. (3) There was no abnormality in the metallographic structure of the blade, and the hardness met the requirements.