Monoazo C.I.PR31 was prepared using 3-amino-4-methoxybenzanilide (red base KD) and 2-hydroxy-3-naphthoyl m-nitroaniline (naphthol AS-BS) as intermediates by diazotization and coupling reaction. Rosin acid was used as surface modification agent of the pigment in the coupling process, then silica dioxide particles with 1~3 layers were coated on the pigment surface by sol-gel method. The samples were characterized by contact angle measurement, SEM, TEM, color capability and thermogravimetric analysis. The results showed that after the pigment was treated by rosin acid, its crystal morphology changed from long strip to disk shapes, and its polarity was obviously enhanced. When the amount of rosin acid was 3% of the total mass of reactants, the contact angle between the obtained pigment and water was 52.8°, the mean particle size and the particle size distribution were 78 nm and 0.01~0.54 μm, respectively, and the pigment sample exhibited good hydrophilic property. The pigments coated with 2 layers and more than 2 layers of silica dioxide with contact angle values of 0° were completely hydrophilic. The introduction of rosin acid made the pigment hues convert into red and blue, while that of the silica dioxide layer made the pigment hues convert into green and blue. The color difference (ΔE) and tinting strength of the pigment sample with 2 layers of silica dioxide, C.I.PR31*-2SiO2, were 0.96 and 105.09, respectively. In nitrogen environment, the pigment crystals began to decompose at 290℃. It is obvious that the pigment reached the standard of high temperature resistant pigment and could be used in aqueous dispersion system.