The uniformity of the heating process about the internal and surface temperature of the slab directly affects the processing quality of the slab. To make the internal and surface temperature of the slab uniform in the heating process, a long heating cycle is needed from street entering to the preheated and the heating section, and to soaking of the slab. But the longer residence time at the high temperature, the surface of the slab is more easily oxided, which is the result of oxidation corrosion of steel at high temperatures and in industrial production is also referred to as “the scale”. In the heating furnace with changes of the air-fuel furnace temperature, flow and process requirements, the temperature of the scale also fluctuated, which played a role in the accurate measurement of the slab surface temperature. Therefore how to separate the slab surface temperature is important. Several image segmentation algorithms are compared to obtain the suitable region growing method, which can distinguish iron scales from the slab temperature and obtain the desired temperature.