Many materials should be leveled when in use, so as to ensure the effect of use. In the process of use, in order to remove the stress in the material, the plate should be leveled. The basic principle of roll leveling is to selectively extend all parts of the material. Below the yield point of the material, the shorter part of the "fiber" of the plate is extended proportionally to obtain a consistent "fiber" length.

In the process of product processing, the realization of the leveling machine is to make the materials bend up and down repeatedly with a smaller radius of curvature when passing through the leveling machine, so as to lengthen the shorter material "fiber". When the sheet moves towards the outlet of the leveling machine tool, the amplitude of up and down bending decreases gradually, so as to eliminate the material deformation caused by severe bending at the leveling inlet of the machine tool. When all the "fibers" on the material are almost the same length, the plate is straight, or "leveled".

In the process of strip cold rolling, the defects of the rolling mill will also cause the thickness of some part of the material cross-section to be lower than that of other parts. Therefore, the thinner part of the material is slightly longer than the thicker part, which makes waves in the longer area, which is not conducive to the later use. Leveling the material is also a very important link.