The work aims to improve seawater corrosion resistance of metal at low cost. New lowcost Al2O3 sol was used to prepare Al2O3 coating on aluminum substrate. Composition, microstructure and wettability of the as-prepared Al2O3 coating was analyzed with X-ray diffractometer (XRD), scanning electron microscope (SEM) and contact angle meter, respectively. Corrosion resistance of the sample was measured and evaluated with electrochemical workstation. The new lowcost Al2O3 sol could be used to prepare amorphous a Al2O3 film on the aluminum substrate, and the film consisted of columns of different diameters; density and diameter uniformity of columns on the film could be altered in the method of boiling water etching. After being modified by low surface energy materials, contact angle between the as-prepared Al2O3 film and deionized water reached 153.2°, and the film had higher hydrophobicity and lower adhesion. The modification improved the seawater corrosion resistance of aluminum substrate, corrosion inhibition rate of the film on untreated substrate was up to 97.9%. The Al2O3 film made from the new lowcost Al2O3 sol on aluminium substrate can effectively improve seawater corrosion resistance.