Abstract: Colloid transport has been shown to facilitate the transport of the contaminants in the subsurface and this process is affected by the attachment/detachment of the colloid. Two models were used in this study to simulate the colloid attachment/detachment behavior, putting focus on colloid transport under different ionic strengths. To represent the colloid attachment/detachment process, the kaolinite suspensions with different NaCl concentrations were applied to soil columns and then deionized water was used to flush the columns. The experimental results indicated that the amount of colloid attachment increased along with the increasing ionic strengths, which is revealed by the breakthrough curves (the decreased peak values). The attachment rate constant K d is positively related to the ionic strength. The simulating results showed that the detachment rate coefficient is significantly related to the ionic strength and the calculated results from the Grolimund’s model for the attachment process agree well with experimental data (R 2>0.95). However, this model can not exactly interpret the detachment process. Reasonable fits were obtained when the colloid transport model is coupled with NaCl solute transport equations which are used to reflect the influence of ionic strength on detachment of colloid (R 2>0.9).