In this paper the destructive interference effect due to nonlinear law of reflection has been analyzed numerically in a wedge shaped zinc telluride slab for total internal reflection quasi-phase matching based second harmonic generation, using ppp polarization configuration. The computer aided simulation indicates 3 dB bandwidth of 360 nm, centred at 8.292 μm, with conversion efficiency of 8.27 %. When the destructive interference effect due to nonlinear law of reflection along with various optical losses are considered, the peak second harmonic conversion efficiency sharply reduces to 1.5 % with a corresponding 3 dB bandwidth of 351 nm, centred at 8.247 μm.