Sodium montmorillonite (MMT) was modified by octadecyl trimethyl ammonium chloride (OTAC) via cation exchange to obtain organo-montmorillonite (OMMT), Al2O3 was treated by KH-550 (3-Aminopropyltriethoxysilane) to get KH-Al2O3. The polyurethane elastomer (PUE) was synthesized with 4,4′-diphenylmethane diisocyanate (MDI), polypropylene glycol (PPG) and 1,4-butanediol (BDO) as the raw materials. And then, OMMT/KH-Al2O3/PUE composite was prepared by the prepolymer method; PUE was the matrix, OMMT and KH-Al2O3 were reinforcements. The micro-morphology and mechanical properties of OMMT/KH-Al2O3/PUE composites were measured and analyzed. The results of FT-IR and XRD showed that OTAC had been introduced into MMT layer and the layer spacing of OMMT had increased. The KH-550 had successfully grafted to the surface of Al2O3 to obtain KH-Al2O3. The TEM results demonstrated the interaction between OMMT and KH-Al2O3, weakening the interaction between the same molecules and the OMMT sheet was further peeled off. The SEM images displayed that a specific ratio of OMMT and KH-Al2O3 had excellent dispersion in the PUE matrix. The mechanical properties of OMMT/KH-Al2O3/PUE composites were significantly better than those of OMMT/PUE and KH-Al2O3/PUE composite. The maximum tensile strength, elongation at break and tensile strength at break are 21.82 MPa, 668% and 19.98 MPa, respectively, which were 43.8%, 29.2% and 36.8% higher than that of PUE matrix, when the content of inorganic components was 3 wt% and the mass rate of OMMT to KH-Al2O3 was 1:1. This composite material is a kind of excellent polyurethane elastomer and widely is maybe used in mechanical accessories, pipe, mining and metallurgy industries. [ABSTRACT FROM AUTHOR]