Based on the lubricating and unsteady properties of rolling processes and hydrodynamic analysis, a film distribution model of the deformation zone which concerns the steady and unsteady conditions is set up and the film wave coefficient is proposed which is used to study the absolute fluctuation of unsteady film thickness. The von Karman equation is used to describe the stress distri-bution of rolling interfaces under the steady and unsteady conditions. According to the stress distribution under the steady condition, the stress wave coefficient is proposed which is used to study and describe the absolute fluctuation of unsteady stress. It is found that large reduction results in a thinner film thickness and a larger hydrodynamic pressure and shear stress in the deformation zone under the steady condition. Under the unsteady condition, as the fluctuation of disturbance factors such as inlet strip thickness intensifies, the film wave coefficient increases, indicating that the absolute fluctuation of film thickness gets larger. The position and value of the pres-sure stress peak change with time under the unsteady condition. The absolute fluctuation of unsteady film thickness has a greater impact on the hydrodynamic pressure than on the shear stress. When the absolute fluctuation of film thickness is 6.33%, the pressure stress and the shear stress have a 1.17% and a 0.24% absolute fluctuation, respectively.