In this paper according to different cooling feafures in the secondary coolingzone,a two-dimensional mathematic model of heat transfer is developed,which is suitable for the op-eration of the casfer in Chongqin g Special Steel Plant,In the model, a finite difference method isadopted and different boundary conditions a different time-step is firstly used.Thus the model isof high precision with a shorter calculation time.The optimum secondary cooling system of the con-tinuous billet can be gained by aimulating and optimizing calculations using the model.