Light gauge channel steel is fabricated from a steel sheet by roll forming. Cut end deformation of the channel steel was investigated by experimentation and three-dimensional finite-element simulation. During roll-forming, concave, convex, and reverse bending deformations on a flange occur and cause bending lines to diverge from the point of contact between the top roll and the flange corner. The reverse bending deformation is caused by a bending moment and a twisting moment. These moments remain on the flange. When the channel steel is cut, the release of the bending moment results in opening at both the top end and the tail end. Then, the release of the twisting moment makes the flange close at the top end and open at the tail end. Deformations at the tail end open widely with the overlap of the two moments.