The cation exchange membrane with high selectivity was prepared by grafting benzenesulfonic acid betaine (SBMA) on the polystyrene-based cation exchange membrane by plasma glow discharge.In order to characterize the modification of the membrane, the SEM, FTIR and chloride ion leakage rates were measured before and after the modification. The results showed that the modified effect was the best when SBMA concentration was 60 g/L, the intensity of plasma irradiation was 0.7 W/cm ², the irradiation time was 7 min, and the irradiation gas atmosphere was argon. After modification, the active groups contained in the membrane were obviously increased and the surface density was uniform. The ion chloride leakage rate of the modified membrane decreased from 14% to 2%.