The scale on the surface of hot rolled steel was removed by high pressure water descaling before rolling in order to gain the good quality of product. If the impact pressure of the water jet is higher, the scale is removed well. However, the temperature drop of the hot rolled steel is increased owing to the flow rate of the water jet. Because it involves many factors affecting the temperature change of hot steel, among which high pressure water for descaling is dominant, it is essential for understanding the temperature change during rough rolling process to determine the subsequent finish rolling technique and analyzing the temperature distribution of the hot steel during the process of the hydraulic descaling. In this study, the relationship between the convective heat transfer coefficient and the impact pressure of high pressure water was investigated by the aid of the experimental data in a reference and FEM numerical analysis. A model for calculating the convective heat transfer coefficient was obtained. A temperature field in 2 050 mm hot strip rough rolling mill of Baosteel was simulated using the model obtained. The calculated surface temperature of steel at the exit of rough rolling train is in good agreement with the measured values.