Abstract: A complex test about the parameters of technique and equipment has performed on roughing roll stands R₂ & R₄ of hot strip mill in WISCO.The rearch of it consists of the relationship between actual motion of rolls and axial forces of rolls on 4H-mills,the forming origins and values of axial forces.Depending on the test data,the actual loading,the mechanism of fracture and the working life of thrust bearing using for back up roll are explored,at the same time,some available steps are suggested to reduce the break of thrust bearings using for back up rolls on stands R₂ & R₄.