Abstract: The crack was appeared at 32 Cr3 Mo1 V roller shell for the aluminum plate casting system in service.The fracture surface topography,metallographic structure,micrograph morphology and chemical composition were analyzed by means of macroscopic observation,optical microscope,hardness testing,scanning electron microscope and EDS（energy disperse spectroscopy）.The results show that the microscopic defects on the roller surface are caused by machining,and molten aluminum permeates into the defects and becomes solidified alumina inclusion, and the harder alumina inclusion inserts into the roller shell inner under the action of the alternate thermal stress and alternate mechanical stress,and then leads to the overall cracking of the roller shell.