Abstract: During the operation of a 330 MW boiler, the drum shaft of the belt coal feeder broke. The reasons for the fracture of the drum shaft were analyzed using macroscopic observation, scanning electron microscopy analysis, chemical composition analysis, mechanical property testing, metallographic examination. The results show that there were more non-metallic inclusions in the drum shaft, which increased the brittleness of the material. There was a turning groove at the root of the variable cross-section of the drum shaft, which increased the stress concentration in that area. Improper hot processing and heat treatment of the drum shaft, as well as abnormal organizational state, resulted in a decrease in material strength and toughness, and an increase in brittleness. Under the action of cyclic torsional load, cracks appeared at the surface inclusions of the variable cross-section retreat groove, and the cracks rapidly propagated in the brittle structure, ultimately led to the fracture of the drum shaft.