The bending deformation caused by chemical strengthening is often thought as a negative factor on the performance of the ultra-thin glass plate. It becomes serious with the thickness of the ultra-thin glass plate getting smaller. The mechanism of the bending deformation was analyzed in this paper. The key factors including thermal history and micro structure variation caused by tin penetration were discussed accordingly. A numerical model was proposed to predict the bending deformation during manufacturing and chemical strengthening procedures. It was validated by bending deformation measurement. It is shown that after chemical strengthening the glass plate bends toward the upper (atmosphere) surface. The tin ion penetration during floating is an important factor to cause bending deformation in chemical strengthening stage.