DL-Homocysteic acid (DLH) is an important free amino acid in central nervous system of human body. In this paper the structure of DLH in D2O solution was discussed. The FTIR and FT-Raman spectra of DLH, which were obtained by Nicolet Magna-IR 750 II FTIR spectrometer and 950 FT-Raman spectrometer, were compared between its solid state and its D2O solution. The results indicated that the H-bonding structure of DLH in solid state was rearranged in D2O solution. The appearance of 1,620 and 1,408 cm-1 suggests the partly ionization of -COOH. From above, we can conclude that a new H-bonding structure of DLH was formed in D2O solution. The H-bond of C-O...H-N was replaced by C-O...D-O, and the H-bonds of -NH3+ and -SO3- were also varied by D2O molecular. Furthermore, the peak shift and the intensity changes of -CH2 in FTIR and FT-Raman spectra were also proved that the skeleton structure of DLH was changed in D2O solution. In addition, this new structure did not alter with the change of concentration of DLH.