Abstract: With the rapid development of China's horizontal continuous casting industry, the quality of mould copper sleeves has become especially critical. Once fracture occurs to copper sleeves, it will cause heavy economic losses. In this paper, the failure analysis for a mould copper sleeve was carried out. The corrosion cracks of the copper sleeve were observed and traced by scanning electron microscopy(SEM) and energy spectrum analysis. The chemical composition and physical properties of a non-failed sample were compared. The results show that the failure of the copper sleeve is stress corrosion failure, caused by the coeffect of the thermal stress in the actual working conditions and the corrosive media in the circulating water, and there is no significant difference in chemical composition and physical properties. Finally, some suggestions were put forward to prevent such failures, such as controlling the quality of the circulating water, improving casting process, and controlling the chemical composition.