Based on the descriptions of the thermal and mechanical behaviors of one peritectic steel solidifying in slab continuous casting mold, including shell shrinkage and deformation, air gap formation and mold flux film distribution in shell/mold gap, and shell temperature profile under the conventional mold taper by a two dimensional transient thermo-mechanical coupled finite element model, a new slab mold taper with non-linear slope narrow face and wedge-shape structures both for the wide and narrow faces corners was presented. The thermo-mechanical behaviors of solidifying shell and the applied effectiveness of improving shell subsurface cracks and reducing the wear of mold copper plate with the new mold taper were discussed. The results show that the mold walls of both wide and narrow faces match the shell shrinkage well under the new mold taper, and both the thicknesses and the distributions of air gap and mold flux film in the gap around shell corner and off-corners are greatly reduced. The shell grows uniformly in the mold. Moreover, the subsurface cracks both in the off-corners of slab wide and narrow faces, as well as the wear of the mold copper plate are also reduced significantly. The working life of the mold is greatly prolonged.