Abstract: In order to accurately simulate the large-scale migration of plutonium in groundwater(a three-phase system), it is necessary to understand the interaction mechanisms between plutonium(Ⅳ), natural colloid, and granite(immobile media). The experimental results show that plutonium pseudo-colloids(i.e., Pu(Ⅳ) sorbed on the surfaces of soil colloids) have the strong mobility(i.e., the recovery percentage of plutonium after plutonium pseudo-colloids transported through columns filled with pore media, R). The mobility R increases with soil colloid concentration ρ(0≤ρ≤375.4 mg/L, 1.3%≤R≤52.5%). The master complexation speciation of Pu(Ⅳ) on the surfaces of soil colloids is \equiv \textSOPu (OH)₃. The speciation percentage(＞95%) is positively correlated with the colloid concentration. The results of experiments and surface complexation calculations confirm that plutonium pseudo-colloids enhance the mobility of Pu(Ⅳ) and thus pose a greater risk of contaminating far-field waters than the dissolved Pu(Ⅳ). The calculations of DLVO interaction potential indicate that the trough depth of the second energy minima(Ф_min2) between colloids and media deepens with increasing colloid concentrations. This attractive interaction potential results in an increase in the adsorptive deposition efficiency of plutonium pseudo-colloids on the media surfaces. The DLVO calculations are consistent with the observation: the mobility of plutonium pseudo-colloids become weak(375.4 mg/L＜ρ≤2017.8 mg/L, 52.5%＜R≤12.7%).