Abstract: 18-high mill has a small diameter of work roll, and the side backup rolls on both sides of the work roll greatly increase the rigidity of the rolling mill and avoid the elastic deformation of the rolls, so it is an ideal equipment for producing thin-gauge strip. In order to investigate the deformation behavior of roll and strip in cold rolling process and to control strip shape with high precision and improve strip quality, a three-dimensional finite element model with equal proportion and high precision was established by using finite element simulation software ANSYS/LS-DYNA and LS-PrePost, taking a 1 250 mm 18-high tandem cold rolling production line of a factory as the research object. Based on the established finite element model, the influence of the position of side backup roll on the stiffness of rolling mill and the shape of each regulating mechanism is systematically studied. The experimental results show that the longitudinal stiffness of the roll system decreases with the increase of the included angle of the roll system, the horizontal displacement of the side backup roll and the transverse displacement of the middle roll; The influence of intermediate roll transverse movement and intermediate roll bending on transverse stiffness is far greater than the other two; The rolling stiffness of work roll is most affected by the horizontal displacement of side backup roll. With the decrease of roll angle, the increase of middle roll transverse movement and the increase of middle roll bending, the strip crown and edge thinning decrease, the strip thickness distribution along the width direction is more uniform, and the control effect of roll angle and middle roll transverse movement on the secondary wave pattern of strip is more obvious.