The infrared reflection spectra (100-4000 cm-1) of the two different polarized components for the single crystals of barium mateborate in the lowe tempreture phase, a new type of nonlinear optical material, at room tempreture are reported in this paper. The transverse and longitudinal frequencies of the fundamental vibration modes in the frequency range above 200 cm-1 are given, and the spectra are analysed in terms of the ‘layermolecular structure' model with reference to the Raman spectra. As a result, the assignment of the inner fundemental vibration modes of the crystals is achieved.