In alloy bar rolling process, the component of alloyed steel influenced the spread coefficient greatly, therefore, the component influence coefficient m of different alloyed steel has been determined firstly to calculate the maximum spread. Then the curvature radius of stress free surface and the “critical point on the contact boundary” have been solved, the surface profile of outgoing workpiece has been obtained. Furthermore, the formula of the equivalent contact section area has been proposed and the mean roll radius has been calculated. The bar rolling experiment and the rigid-plastic FEM (finite element method) simulation have been carried out to verify the novel approach. Compared with experimental data and simulation results, the novel approach can be used in setting processing parameter and design of finishing groove. In alloy bar rolling process, the component of alloyed steel influenced the spread coefficient greatly, therefore, the component influence coefficient m of different alloyed steel has been determined first to calculate the maximum spread. Then the radius of curvature of stress free surface and the “ critical point on the contact boundary ”has been solved, the surface profile of the outgoing contact has been obtained. rigid-plastic FEM (finite element method) simulation have been carried out to verify the novel approach. Compared with experimental data and simulation results, the novel approach can be used in setting processing parameter and design of finishing grooves.