Abstract: The causes of cracking in Inconel 601 alloy during hot reaming were analyzed by OM, SEM, FEM and thermodynamic equilibrium phase diagram. The results indicate that the microstructure of Inconel 601 alloy is single austenite and no harmful precipitation phase in the hot reaming temperature. The radial metal flow and stress distribution of the billet are not uniform during the hot reaming, and the high tensile stress exists on the outer surface. The non-uniformity of initial microstructure is the main cause of hot reaming crack. Improving the microstructure uniformity of billet and reducing the expansion ratio can avoid the hot reaming cracks.