It has been demonstrated by researchers that the β-form is beneficial to toughness and ductility. In our previous work, the β-nucleation agents (β-NA) was compulsively distributed in specific layered spaces of PP matrix through the microlayered coextrusion to form layered samples, where polypropylene (PP) and β-nucleated polypropylene (β-PP) layers alternately aligned along the extrusion direction. During the isothermal crystallization, β-transcrystallinity (β-TC) in the PP layer was induced by β-NA located on two dimensional layered interfaces and grew vertically to the interface. The layered samples with high content, continuous and highly ordered β-TC exhibited excellent mechanical properties, which were necessarily relevant to the special structure and morphology of β-TC. In this study, samples with different content of β-TC were prepared through the microlayered coextrusion by adjusting the thickness ratios (r) of PP and β-PP layers, namely the unstratified sample with will-developed β-spherulites (Un), layered sample (r=1) with certain content of β-TC (L(1/1)) and layered sample (r=3)with high content of β-TC (L(3/1)). In this work, the phase transformation and structural evolution of β-TC during uniaxial stretching was investigated by differential scanning calorimeter (DSC), Polarized optical microscopy (POM), scanning electron microscopy (SEM) and wide-angle X-ray diffraction (WAXD). During stretching, the β-TC in layered samples was found easier to transform than β-spherulites and intended to transform into α-crystal at high strain. The results of microscopic observation indicated that the lamellae of β-TC transformed to other phases later than β-spherulites because the horizontal lamellae (parallel to the stretching direction) in spherulites were first stretched to break. Eventually, the toughening mechanism of β-TC was attributed to extraordinary transformation behavior of β-TC and the structural evolution of lamellae during deformation.