The elastic-wave transfer function method (ETFuM) was applied to make clear the micromechanism of the deformation process during dynamic tensile testing of polymethylmethacrylate (PMMA) and polycarbonate (PC). In PC, the transfer function began to change at a high frequency. After that, it decreased abruptly in the low-frequency region. The variation of the transfer function at high frequency was caused by the nucleation and growth of microdefects such as crazes and microcracks. The variation at low frequency was caused by plastic deformation such as inclined necking and microdefects due to shear stress. On the other hand, in PMMA the transfer function changed homogeneously with elongation at high frequencies and did not change at low frequencies. The variation of the transfer function during tensile testing related to the micromechanism of elastic and plastic deformation processes in both PC and PMMA. The results suggested that the ETFuM is a useful and powerful method for evaluating the micromechanism of deformation processes in polymers in a non-destructive and dynamic way.