Abstract: The causes of cracking of 1Cr13 semi-martensitic stainless steel shaft after heat treatment were analyzed by means of macroscopic morphology examination, chemical composition analysis, metallographic examination, hardness test and fracture morphology analysis.The results show that the main reasons for the cracking of 1Cr13 short shaft are the carbon content slightly higher than the standard value, the existence of more sulfide inclusions in the microstructure with inhomogeneous distribution and poor morphology control, the segregation lines formed by pore air channel segregation and carbide aggregation segregation, and the residual stress after quenching, sulfide inclusions and segregation lines distributed in long and thin strips are the most harmful. Finally, the cracking problem of 1Cr13 semi-martensitic stainless steel shaft after heat treatment is strictly solved by controlling the chemical composition, the quantity, size and distribution of inclusions and segregation lines of the steel and heat treatment process.