At room temperature, the mid-infrared spectra of geometrically frustrated natural atacamite (hydroxyl copper chloride, β-Cu2(OH)3Cl) in the range of 4 000~400 cm-1 were measured by FTIR spectrometers, and meanwhile its Raman spectrum in the range of 4 000~95 cm-1 was obtained by Jobin Yvon LabRAM HR800 Raman spectrometer. According to its crystal structure parameters, the authors confirmed the characteristic peaks of sample 4 000~2 500~1 000 cm-1 in the functional group region and 1 000~550~200~95 cm-1 in the fingerprint region, and also explored its microscopic origin. Five distinct regions were assigned: the hydroxyl stretching vibration νO—H determined by the overall environment around the hydroxyl group; the overtones generated by the sum or multiplication of fundamental frequencies of hydroxyl bending vibration; the hydroxyl bending vibration modes δO—H of the combination of δCu—O—H and δO—H…Cl; the vibration modes of strongly bonded planar CuO4 units; the vibration modes of weakly bonded linear-triatomic chain Cl—Cu—O/Cl. The bands were assigned in accordance with its crystal structure parameters, which is more reasonable to establish the relationship between its molecular structure and its respective spectral properties.