The raw material - residue of oil production from Huadian oil shale - was modified with cationic surfactants; the hydroxyl groups on the aggregated silica surface were alkylated directly. The structure of alkylated Si-hydroxyl on modified silica surface was characterized by means of infrared spectroscopy, nuclear magnetic resonance analysis, thermal gravimetric analysis and scanning electron microscopy analysis. The results showed that modification rate of hydroxyl groups on the surface of the modified silica obtained was about 84%. The modification conditions were optimized basing on application of the orthogonal experimental method, and the optimum parameters were as follows: the reaction temperature of water medium - 40 degrees C, pH value within the range of 9-10, and the molar ratio of cationic surfactant to silica hydroxyl on the surface - 2:1.