Mobile colloid may play an important role in the transport of contaminants in soils and ground water, especially for strongly adsorbed heavy metals. Effect of colloid SiO₂ on transport of Cd in saturated soil was studied in an indoor soil column and effluent experiment. Results of the experiment were simulated numerically with the CDE (convection-dispersion equation). It was found that the colloid inhibited mobility of Cd, making it spend longer time getting through the column and lower in concentration in the effluent and that Cd adsorption was mainly controlled by dynamic reaction. The OSM (one site nonequilibrium model) coupled with the Freundlich isothermal adsorption could better simulate Cd transport in the loamy sand soil. The Cd adsorption feature parameter β obtained through simulation was quite small which indicates that the adsorption surface of the soil was rather nonuniform. SiO₂ colloid penetrated the column pretty quickly. Its transport in the soil could well be described with the CDE coupled with kinetic attachment-detachment reaction. As affected by colloid, the CDE could successfully simulate transport of Cd in the soil with SiO₂ in presence. Meanwhile the parameter sensitivity analysis indicated that the smaller the k_amc and the k_aic , the larger the k_dmc and thek_dicand the more convenient the transport of Cd.