Abstract: This paper presented the Mid-IR photoacoustic spectra of polyphenylene sulfide (PPS) which was first measured by us and the group theoretical analyses. By treating the chemical unit, C_6H_4S_2, as the characteristic unit for PPS chains, the group classifications and the normal mode constructions by the internal coordinates and projection operator technique were carried out successfully, also, the correlation analysis between PPS and benzene moleeule was performed to further aid the spectral assignments. This work was the basis upon which further studies of the PPS composites may proceed.