In order to analyze the effects of OMMT on PU mechanical properties，polyurethane(PU) was synthesized by diphenylmethane diisocyanate(MDI)，polyether diol，diethylenetriamine and organically modified montmorillonite(OMMT) through in-situ polymerization. The structure of the modified PU was characterized by FTIR. The dispersion and structure of OMMT in the matrix were studied by SEM. The influences of the OMMT on theproperties of the PU matrix were investigated by the change of shear strength，peel strength，tensile strength and elongation at break. The results showed that the most of OMMT was fully exfoliated into individual layers and uniformly dispersed in the polystyrene matrix，interlayer spacing of OMMT was increased. The addition of OMMT improved the integrate capability of the PU，the best comprehensive performance of OMMT/PU can be achieved whenthe content of OMMT is 4wt%，the maximum shear strength of the OMMT/PU was 8MPa，that was increased by29% than that of pure PU(22. 13MPa)，the tensile strength was 283.1 MPa，that was increased by 71%than thatof pure PU(165 MPa)，the elongation at break was 569%，that was increased by 41%than that of pure PU(403%).