Abstract: Based on “functional montmorillonite” concept, intercalated and exfoliated polystyrene nanocomposites were prepared by magnetism mixing and ultrasonic mixing. The XRD and TEM results show that ultrasonic mixing favors the dispersion of organicclay in polystyrene, and wellexfoliated polystyrene nanocomposites can be prepared. Based on the paramagnetic effect of Fe3+ in the MMT layers on the relaxation time of protons (TH1), the exfoliation degree of the nanocomposites were investigated by proton relaxation experiments. The NMR result proves that TH1 decreases with the clay dispersion degree increasing and the dispersion degree of organicclay in the polymer can be determinated by the TH1 values quantitatively. The NMR relaxation result is in good agreement with the TEM result.