Abstract: The total heat exchange factor method is used as core model for L2 control system of reheating furnace. Total heat exchange factor is not only a function of structure parameters， but also a function of operating parameters， thus the identification for it is hard. Based on the drag thermocouple experiment of No3 reheating furnace in 2050 hot rolling mill in BaoSteel， basic identification was researched. The experiment data were arranged. Meanwhile， CF was identified by surface temperature gradient method. Finally， complete expression of the identification system was derived， and the result of basic recognition was analyzed. In the process of identification with a large number of sampling points， the surface heat flux curves appeared oscillating. It was caused by the mismatching between sampling period and system resolution. The CF curves show that the values of CF at the same site are different when the slab is still. So the compensation for CF is necessary.

Key words: total heat exchange factor, drag thermocouple experiment, surface temperature gradient method, basic identification, experience furnace temperature