Abstract: The reason for large area spalling on the surface of high speed steel composite roll was analyzed by chemical composition analysis, mechanical property testing, microstucture and fracture morphology observation. The results show that the improper control process of three time pouring and low purity of core ductile iron liquid led to the generation of a large number of serious defects such as the coarse carbides, loose pore defects distributed in sheets and inclusions distributed aggregatively at the interface between the middle layer and the high speed steel surface layer and the core cast iron layer of the composite roll, resulting in poor bonding at the interface. Under rolling force, the crack initiated at the these defects and rapidly expanded along the defects, ultimately leading to large area spalling failure on the surface of the roll.