For understanding the phase and transfer properties of optical wave propagating through negative refractive index medium (NIM) layer, the relations between negative refractive index, the value and direction of wave vector k, the coordinates and the phase have been investigated intensively. The results prove the peculiar direction of the wave vector k in a NIM layer results from its negative scalar magnitude. In the identical right??hand coordinate system within NIM and PIM layers, only this negative scalar needs to substitute in the numerical simulation, while the vector k should be determined by both the negative scalar and the unit vector k0(k0>0). Based on this analysis, a transfer matrix of optical waves in NIM layer has been derived. The primary results show that the spectra characteristics of TE and TM modes from the films comprising NIM and PIM layers have changed prominently.