Abstract: The function of stage-cooling in flatness control becomes more important than ever before by many examples in factories. On the base of the convection heat transfer between the working rolls and the coolant fluid of the aluminum mill 1400F, the optimum values of convection heat transfer were found through orthogonal experiments and proved to be optimal by numerical simulation. The factors in orthogonal experiments arranges as the viscosity, the speed, the temperature and the spraying angle of coolant fluid in the order of importance.