The present invention discloses a lipophilicity modification method of nanometer alumina. The lipophilicity modification method comprises: dispersing nanometer alumina in water to prepare a nanometer alumina-water dispersion liquid, adding fatty acid having a carbon number of more than or equal to 8 to the nanometer alumina-water dispersion liquid, carrying out a stirring reaction under a constant temperature condition to complete lipophilicity modification, and carrying out slid-liquid separation to obtain the solid, ie., the surface modified nanometer alumina. According to the present invention, the process is simple, the operation is convenient, the grafting rate of the obtained product can be up to more than 15%, the dispersion property, the compatibility and the stability of the nanometer alumina in the organic system are improved, acids, alkalis or any organic solvents are not used in the reaction process so as to recycle the water, and the preparation process is safe, environmentally friendly, economical and efficient.