Pollution of groundwater and soil by heavy metals and organic substances is getting increasingly serious. In the polluted soil or water, the pollutants often exist simultaneously, to remedy the soil or water, the method of fixation through adsorption is one of the most effective ways. Organically-modified soils can effectively adsorb organic compounds. Amphoteric surfactant modified soils can adsorb organic substances and heavy metals at the same time, but their organic pollutants adsorption capacity is not so high as cationic modified soils. In order to enhance their capacity, they are further modified with another type of surfactant modifier. For that end, bentonite was modified with dodecyl dimethyl betaine (BS-12) + Tween20 complex varying in ratio by wet chemical method and effects of the modified bentonites adsorbing Cd² relative to ratio of the modifier (in terms of total carbon ratio of Tween20/BS-12, set at 0.25, 0.5, 1 and 1.5), temperature (20，30 and 40℃), pH (3, 5 and 7), ionic strength (0.05，0.10 and 0.50 mol L^-1) were explored using the batch experiments and control variate method, and mechanism of the adsorption was studied from the aspects of adsorption isotherms (Model fitting, using the CurveExpert 1.4 nonlinear fitting software and the stepwise approximation method for nonlinear fitting), temperature effects and thermodynamics. Results show that the equilibrium Cd² adsorption capacity of Tween20 complex modified bentonite varied with modification ratio, displaying an order of BS 0.25T > BS 0.5T > BS > BS 1 T > BS 1.5 T > CK, which means that when the ratio ranged between 0 and 0.5, the capacity rose with the ratio, but when the ratio exceeded 0.5, the capacity decreased with the rising ratio, which demonstrates that the Tween20 modification ratio, less than 0.5, is in favor of Cd² adsorption on modified bentonite. The adsorption isotherms of Cd² on modified bentonite can be described with the Langmuir model. Within the experimental range that ensured Cd² soluble, the rise of pH under the acid condition increased Cd² adsorption, somewhat, as a result of strong competition between H and heavy metal ions for adsorption sites. Ionic strength has some strong impacts on Cd² adsorption capacity of the modified bentonite, mainly in three ways: (1) Forming ion pairs or affecting pH of the solution, thus altering the activity of free metal ions; (2) Triggering competition between K and Cd² for adsorption in the supportive electrolyte; (3) Causing the supportive electrolyte to compress its double electrical layer, i.e. diffusion layer, thus altering the adsorptive surface of the soil sample, As a result, the soil sample weakened its Cd² adsorption under increasing ionic strength. With rising temperature, the modified soil increased its Cd² adsorption, showing a positive relationship. Thermodynamic parameters show that Cd² adsorption on modified bentonite is a entropy controlled spontaneous process. Cd² adsorptions on all the soil samples are endothermic processes. It can, therefore, be concluded that modification of amphoteric bentonites with Tween20 to a certain ratio can increases the soil Cd² adsorption capacity; amphoteric modifier BS-12 and nonionic modifier Tween20 are used jointly to modify bentonite, altering its electrical attraction and hydrophobic bonds, thus increasing negative charge of the surface layer and thickness of the hydrophobic layer of the bentonite. When Tween20 modification ratio is low, the interlayer spacing expands in bentonite, thus leading to increase in Cd² adsorption, while higher modification ratio brings about a thick layer thickening, blocking negative charge sites on the surface of the modified soil, thus lowering the soil’s Cd² adsorption capacity.