Rolling force is the most important technical parameter for the tandem cold mill. In this paper, the precise models and calculation process for the rolling force are introduced. The rolling force model is based on the Bland-Ford and Hill theory, and the roll flatten radius is calculated with the Hitchcok’s formula. The deformation resistance of the strip is calculated with the model, whose parameters are decided according to the steel grade. The friction coefficient model is built according to rolling speed and rolled length of the roll. The rolling force and the roll flatten radius are calculated with the iterative method. These models are used for online process control of one five-stand tandem cold mill. Comparing the calculation result and the actual data, the precision of the rolling force calculation is high.