Abstract: Non-conformance of impact energy is checked out with a whole batch of the Φ244.48 mm×11.05 mm N80-1 casing,and after quenched the non-conformance status still remains. The causes for the non-conformance are analyzed. It is identified via the analysis that the main cause for the non-conformance is the existence of the banded structure and the MnS inclusion. Accordingly it is suggested to take relevant actions to ensure qualified impact energy of the rolled N80-1 casing,including enhancing control of the melting process,reducing the chemical composition precipitation,reducing the level of the banded structure,improving steel clearness,and lessening the inclusion content.