Abstract: The fracture causes of 45 steel shaft seat during service process were analyzed, and the metallography, chemical composition and fracture morphology of the shaft seat were observed. The results show that the fracture surface of 45 steel shaft seat is mostly cleavage plane, showing typical brittle fracture characteristics, and there are a few secondary cracks in local area. The microstructure of the fracture axle is mainly composed of Widmannstatten structure, acicular ferrite and lamellar pearlite structure. The macroscopic chemical composition meets the standard requirements, and there is a very small amount of oxide inclusion in local areas. The brittle Widmannstatten structure is the main cause of shaft seat fracture.