In this paper, according to the principle of grain refining and semisolid forming by cooling sloping plate process, the distributions of boundary layers during melt treatment by the sloping plate are studied, and mathematic models of heat transfer and cooling rate are established. Calculation results show that the change time from laminar flow to turbulent flow decreases with the increases of the sloping angle and initial flow velocity. The thickness of temperature boundary layer decreases with the increases of initial flow velocity. The effect of the sloping angle on the thickness of temperature boundary is small. The boundary layer thicknesses of the both temperature and velocity increase with the increase of the flow distance gradually. In the laminar flow region, the thickness of the temperature boundary layer is much bigger than that of the velocity boundary layer, while the two layers coincide with each other in the turbulent flow zone. The melt cooling rate on the sloping plate and the melt thickness have an inverse proportion relationship between each other. When the initial flow velocity is lower than 1 m/s the cooling rate increases along the sloping plate gradually. While the initial flow velocity is 1 m/s, the cooling rate dose not change approximately. However, when the initial flow velocity is larger than 1m/s the cooling rate decreases along the sloping plate gradually. The melt cooling rate on the cooling sloping plate is between 100 K/s and 1000 K/s, which belongs to meta-rapid solidification scope.