Abstract: With benzoyl peroxide as initiator,a series of styrene-maleic anhydride copolymer was prepared by solution copolymerization under different temperatures.Polystyrene-maleic anhydride sulfonic acid sodium(SSMA) with different relative molecular mass was obtained by sulfonated the polystyrene-maleic anhdride.The dispersibility of 20% diflubenzuron suspension concentrate was identified by assaying and analyzing the diameter of particles,Zeta potentials and viscosities.The results showed that the optimal dispersant was SSMA,which was prepared at 75℃,and the most suitable concentration was 3%.At pH=9,the dispersion stability of suspension concentrate was the best due to the strong steric hindrance provided by completely ionizing of the molecules.Na⁺ or Ca²⁺ was able to decrease the absolute value of Zeta potential by compressing the electronic double layer thickness of particles surface,which could lead to particles aggregation due to the reduction of electric quantity and ultimately deteriorate the dispersive effect of suspension concentrate.If the ions concentration were the same,the coagulation capacity by Ca²⁺ was stronger than that of Na⁺,and the dispersion stability of suspension was worse after adding Ca²⁺.