Abstract: A medical stainless steel cutting anastomat anvil was broken during the operation. The causes of fracture were analyzed by means of macroscopic observation, macroscopic examination, chemical composition analysis, scanning electron microscopy and energy spectrum analysis, mechanical property test and metallographic examination. The results show that the fracture mode of the anvil was intergranular brittle fracture, and the improper tempering temperature control was the root cause of the fracture of the anvil. The first type of temper brittleness was produced during the tempering process, and serious segregation occurred at the grain boundaries, which eventually led to a significant decrease in the impact toughness of the material.