Abstract: Aiming at H-beam straightening, the plastical deformation of H-beam flange should be occurred when the rollers pressed the web plate. In order to avoid flaws in the process of H-beam straightening, an adequate mechanical model was established and the relations between bending moments, forces and bending deflections of the H-beam in nine-roller straightening were deduced. The range of the technological parameters such as forces and bending moments under each straightening roller was determined by adjusting the bending deflections in practice.