Due to the complexity of the actual rolling process, asymmetrical conditions of deformation zone can cause front end bending or lead to poor shape, profile or quality of the product, as well as reducing productivity. Therefore it is important to study the geometric parameters of deformation zone in order to determine the work parameters accurately during rolling. Because the stock is often inclined when it enters the rolls, the deformation zone is asymmetrical. In this investigation, a model of calculating contact length between stock and roll precisely is deduced according to the theory of rolling. The results by theoretical calculation and experiment prove that the projected arc is raised while the stock enters the rolls serious asymmetrically, as well as the increase of the entrance thickness of the rolling stock and the decrease of the exit thickness of the rolled stock.