Abstract: The critical micelle concentrations(cmc,1×10^-5 mol/L) and the surface tensions(γ_cmc,mN/m) of nine alkyl aryl sulfonate composite systems were measured at 25℃.The relationship between composite system relative molecular mass and its distribution and surface properties was studied.The γ_cmc and cmc values of five distributions with the average relative molecular mass of 432 were determined as 2.341 and 28.96 for the incremental type molecular mass distribution;2.458 and 32.56 for the descending type distribution;3.667 and 36.14 for the normal type distribution;2.201 and 27.55 reverse normal type distribution;and 2.761 and 33.54 for the uniform type distribution,respectively.Moreover,the γ_cmc and cmc values for the descending distribution with four average relative molecular masses were determined as 3.786 and 29.54,3.530 and 29.81,2.458 and 32.56,8.337 and 29.54 for average relative molecular mass of 390,418,432 and 446,respectively.The adsorption capacity,Γ_max,the saturated adsorption area,A_m,and the surfactant concentration needed in order to reduce surface tension by 20 mN/m(pC₂₀) were calculated according to Gibbs adsorption equation and a reasonable explanation was also presented.