Organo-mineral complexes play an important role in soil. Clay mineral-polysaccharide complex is a precursor, contributing to the formation of clay Organo-mineral complexes, but its specific functions remain unclear. Montmorillonite-xanthan complex was prepared and analyzed for its structure with X-diffraction and spectra at various depths with a Fourier transform infrared photoacoustic spectroscop (FTIR-PAS) that has the function of in-situ step-scanning. Results show that the interaction between montmorillonite and xanthan occurred mainly on the surface of montmorillonite, and subsequently formed an interfacial layer, which featured a distinct infrared photoacoustic spectrum; the formed complex demonstrated stronger water-holding capacity than montmorillonite, and its surface differed significantly from its subsurface in spectrum, and the interfacial layer of the montmorillonite-xanthan complex was approximately 2.05~6.47 µm thick according to the step-scanning with FTIR-PAS.