Temperature difference between the center and the surface of hot rolled flat after rapid cooling results in heat transfer from the center to the surface, which causes the surface temperature rise in a short time. The flat cooling experiment has been carried out to measure temperature changing on the surface and interior of flat during water cooling process and after that. FEM has been used for simulating temperature rise phenomenon for different thickness under various cooling conditions. The cause of temperature rise has been analyzed, critical condition for the occurrence of temperature rise has been confirmed, and the duration of temperature rise and the value of temperature rise under various conditions have been obtained. The results indicate that both the duration and the value of temperature rise increase with the increment of temperature difference between center and surface caused by the increase of thickness and cooling rate.