In the cold strip rolling process, tension plays a great role in the stability of rolling, reduction of rolling force and power consumption, coordination of thickness control, and improvement of flatness quality. The correcting and attenuating effect of tension on flatness deviation is gradually revealed, but quantitative analysis of their inherent effect is still insufficient. Thus, a roll-strip-tension coupling model with both accuracy and efficiency was established to analyze the influence of tension on flatness deviation. In the model, a strip plastic deformation model based on a 3-dimensional differential method was corrected by a strip transverse flow factor obtained by an finite element method simulation model and was consequently combined with a rolls elastic deformation model based on the influence function method and the tension calculation module. By the coupling model, the mechanism of the self-correction effect of front tension and the attenuation effect of back tension on flatness deviation was further discussed, and the calculation results of the corresponding correction coefficient and attenuation coefficient were obtained. The present paper brings more insight into the effect of tension on flatness, and lays a foundation for the optimization of the shape control model in the cold rolling process with tension.