Abstract: A trimericationic surfactant(Ⅲ-12-4) was prepared by ring-opening and quaternization reactions from epichlorohydrin, tertiary amine and glycerin with water as the solvent. The yield of Ⅲ-12-4 was 86.9%. The surfactant was characterized by MS and elemental analysis. The surface properties of Ⅲ-12-4 and sodium dodecyl sulphate(SDS) mixing systerm were determined by means of surface tension measurement using DSC apparatus. The development of micropolarity and the micelle aggregation number(N_m) of Ⅲ-12-4/SDS were assesed by steady fluorescence prob method. The results indicated that compared with monosurfactant system, the mixing systerm exhibited lower critical micelle concentration(cmc) and more effective surface tension reduction, showing synergistic effect. When n(Ⅲ-12-4):n(SDS)=3:7, the critical surface tension(γ_cmc) and critical micelle concentration(cmc) were 16.95 mN/m, 1.33×10^-5 mol/L respectively, and the micelle aggregation number was 1/6 of that of SDS. The mixing micelle was more compact. Micropolarity was lower.