Abstract: Based on hydrodynamics， rolling theory， and characteristics curve solution of Hill differential equation， a dynamic model of unsteady film thickness distribution at the rolling interface was constructed. The model considered the fluctuation of the inlet strip thickness and the roll radius. The film wave coefficient was proposed to reflect the absolute fluctuation of film thickness. The corresponding simulation and analyses were also carried out. The results show that the film thickness distribution and the thinnest film thickness are timedependent under unsteady condition. As the nonuniform degree of inlet strip thickness and the roll radius increases， the absolute fluctuation of film thickness rises. However， the fluctuation frequency shows little effects on the absolute fluctuation of film thickness.

Key words: cold rolling, unsteady state, rolling interface, lubrication, film thickness distribution, film wave coefficient