Shallow deep drawing process of a square cup is investigated in this paper. A combined friction model is introduced which integrates the Khonsari's friction model based on asperity contact and Wilson's friction model based on lubricant flow. A film thickness ratio of 0.035 is introduced for 0.15 mu m standard deviation of surface summits. Below the ratio of 0.035, Khonsari's model gives more accurate results since asperity friction is dominant. Above the ratio of 0.035, Wilson's model gives more accurate results since hydrodynamic friction is dominant.