According to the case of billet heating in a regenerative type heating furnace, the temperature distributing of billet about upper surface, undersurface and center surface in length and width is studied by computational fluid dynamics (CFD)in this article, and the questions of billet such as different temperature of upper surface and undersurface, the higher temperature of foursquare margin and the lower temperature of tapping orifice are put forward. The relation of different thick billet and the heating time is simulated and studied, the result of simulation and the heating time in the actual heating furnace is compared, and the expressions of thickness and heating time is educed by numerical suit, and put into production. The above result of study can offer foundation for the establishment and optimizing of billet heating system.