A mathematcal model of heat transfer between the billet and the roller for the seeondary cooling zone in billet continuous casting is established. By means of the simulated test,a regres sion relation between the heat flow from the billet into the roller and the surface temperature and cast ing speed and spray water density obtained. The calculated theoretical values for change of surface temperature are in agreement with the measured data, these studies may contribut to the quantitative analysis and the calculation of the heat transfer of the secondary cooling zone.