The active branched chain (IP550) with primary amine was synthesized by isatoic anhydride (IA) and methoxypolyethylene glycols550 (MPEG550). The comb-like modified polymer surfactant (SMA-IP550) was prepared by amidation reaction between styrene-maleic anhydride copolymer (SMA) and IP550. The synthesis process of products was investigated and the chemical structure of SMA-IP550 was characterized by FTIR and 1HNMR. The results showed that the IP550 with 79.3% yield were achieved when the conditions were controlled as the amount of catalyst(4-dimethylaminopyridine) 0.9% based on the total mass of reactants, the molar ratio of IA to MPEG550 1:1, reaction temperature 120℃ and reaction time 30 min. The modified SMA(SMA-IP550) with 42.5% grafting yield was obtained when the temperature was 140℃, the molar ratio of IP550 to MA was 0.5:1, the solid content was 30% and the reaction time was 2 h. By comparing the dispersion, viscosity reduction, emulsification and wettability of modified SMA with different branched-chain lengths, the results showed that the structure of comb-like modified styrene-maleic anhydride copolymer can be adjusted, which was closely related to the emulsification and dispersion.