Abstract: A large cylindrical part of 30CrMnSi steel cracked during spinning process. Through macroscopic observation, chemical composition analysis, fracture analysis, microstructure observation, scanning electron microscope and energy spectrum analysis, and conbined with inspection of production process. The reasons for cracking of cylindrical part were analyzed. The results showed that improper heat treatment process of cylindrical part before spinning led to uneven hardness and structure. This was the main reason for spinning cracking of cylindrical part. By improving heat treatment process, the two-way alternating cooling method suitable for large workpieces was selected. In addition, the spinning process was improved and perfected. After that, no cracks occurred in spinning products, and product performance met technical requirements.