This study aims to clarify the breaking behavior during wedge shearing process of an aluminum worksheet that stacked on to an underlay sheet. One of the problems faced in wedge cutting process is the separation possibility and the quality sheared profile of worksheet, the lower underlay sheet was introduced. To study the breaking behavior of an aluminum sheet with flexible underlays, a 42°center bevel blade indentation test to a 0.39mm thickness aluminum stacked on to several flexible underlays conditions were carried out experimentally and numerically. For discussing the effect of the rigidity of underlay on the breaking behavior of worksheet, an elasto-plastic finite element analysis was applied to. The following were obtained: (i) the initial breaking of worksheet and the sheared profile depends on the underlay rigidity; (ii) the breaking propagation is started from the lower surface of worksheet and grows up to the upper side beneath the tip edge.