Heat transfer of flow melt and grain refining mechanism during melt treatment by the cooling sloping plate were investigated.The results show that the cooling sloping plate can refine not only grains of alloys but also can obviously refine pure metal.Cooling ability of the plate is the key factor that induces grain refining,the plate material and the flow amount can affect cooling rate of the melt and thus affect refining effectiveness.The cooling rate of the melt on the cooling sloping plate is much faster than that of the conventional casting process,which can reach 1000 K/s and belongs to meta-rapid solidification scope.The thickness of the temperature boundary layer is much larger than that of the velocity boundary layer on the sloping plate,but the temperature gradient is small in the temperature boundary layer.Under strong cooling action by the cooling plate,most parts of the melt on the plate surface can form undercooling,which causes continuous eruptive nucleation,this is the main grain refining mechanism,and the heterogeneous nucleation on the plate surface is a helpful supplement for the nucleation. Heat transfer of flow melt and grain refining mechanism during melt treatment by the cooling sloping plate were investigated. The results show that the cooling sloping plate can refine not only grains of alloys but also can refine refined pure metal. Cooling ability of the plate is the key factor that induces grain refining, the plate material and the flow amount can affect cooling rate of the melt and thus affect refining benefit. The cooling rate of the melt on the cooling sloping plate is much faster than that of the conventional casting process, which can reach 1000 K / s and belongs to meta-rapid solidification scope. The thickness of the temperature boundary layer is much larger than that of the velocity boundary layer on the sloping plate, but the temperature gradient is small in the temperature boundary layer. Under strong cooling action by the cooling plate, most parts of the melt on the plate surface can form under cooling, which causes continuous eruptive nucleation, this is the m ain grain refining mechanism, and the heterogeneous nucleation on the plate surface is a helpful supplement for the nucleation.