In order to further understand the synthesis and biodegradation mechanism of L-arabinose during the course of metabolism, terahertz time-domain spectroscopy and laser Raman spectrometer were used to measure the vibrations of their groups in this paper. The results shows that: in the frequency range of 5～85 cm-1 frequency range, The 49.5 and 72.2 cm-1 vibrational peaks were detected and the two vibrations were in agreement with the frequencies of anomalous dispersion in the curve of refraction index, the second peak was detected for the first time. Therefore, the two vibration peaks could be as characteristic absorption peaks of L-arabinose because of their strong absorption. To the most, the wave type of terahertz spectra in this range was very similar to the theoretical wave type of the simple combinations of the three isomers, and the sample was not a single component, but a mixture of three isomers. Raman spectra showed that vibrations of L-arabinose were concise and clear and that vibrations in fingerprint frequency ranges were divided into four characteristic vribrational regions(from high to low): stretching vibrations of bonds in pyran cycle, rocking of methylene, twisting of H—O in cycle and torsions and deformations of cycle skeleton, including puckering. The vibrations of α-, β- and open chain isomers were calculated by B3LYP/6-311G** according to DFT, respectively. The vibrations of the three isomer were assigned by potential energy distribution. Comparisons between observed and theoretical curves were that frequencies of theoretical curves showed red shift for vibrations of L-arabinose and the exact causes must be confirmed by further tests.