Hydrophobic Al2O3 membrane can be prepared by adding diethoxy dimethyl silane (DDS) through sol-gel method using aluminum isopropoxide as raw material. Influence of DDS content on the structure and properties of the Al2O3 membrane were studied. Structure, wettability, thermal stability and surface morphology of hydrophobic Al2O3 membrane were analyzed by infrared spectroscopy(IR), contact angle, thermogravimetric analysis(TG-DTG) and atomic force microscope (AFM). The results show that the hydrophobic group-CH3 of Al2O3 membrane surface is rich when the optimal content of DDS is 5%, and the membrane has good hydrophobicity with 118° contact angle; as the temperature increased, the hydrophobic properties of the membrane reduced, the reason lied in the decreasing of hydrophobic -CH3, so the optimum sintering temperature is 200℃; the membrane surface has slight roughness.