A novel polymeric dispersant (SMG) was prepared by modifying copolymer of styrene and maleic anhydride (SMA) with the epoxypropyl trimethyl ammonium chloride (ETA) through interface reaction. Fourier transforms infrared spectroscopy (FTIR) indicated that the epoxy groups had reached with the anhydride groups. 30.96% anhydride groups in SMA was taken part in the reaction when molar ratio of ETA to SMA was about 1.3, mass ratio of p-toluene sulfonic acid to SMA was 14%, the reaction temperature was 78℃ for 6 h. SMG can be used as dispersant for carbon black and showed an excellent dispersing ability when modification degree was higher than 14%, the mass ratio of SMG to carbon black was about 7%, and pH value was about 9. The prepared carbon black dispersion had an excellent stability to temperature, which the change rate of particle size was only about 3.6% when it was treated at 60℃ for 24 h. The zeta potentials of carbon black dispersed by SMG was about 28.16mv when pH value was 3, and was taking some negative charges when pH value was higher than 6.5.