Abstract: Plutonium is a highly toxic transuranic element in high-level radioactive waste. Because of the variety of species of plutonium, it has a serious potential to migrate to the ecological environment in the process of deep geological disposal. The deep geological disposal project of high-level radioactive waste needs to solve the key problem of how to prevent the release of plutonium into the biosphere. Bentonite is considered by many countries as a buffer material for deep geological disposal of high-level radioactive waste due to its high adsorption, low conductivity, chemical buffering, and mechanical stability. Colloid is a very important factor in the adsorption and migration of radioactive pollutants. The main sources of colloids in groundwater are underground minerals, hydrolysis of metal ions produced after the dissolution of underground minerals, underground humic acid complexes and colloids formed by radionuclides (hydrolyzed polymers such as plutonium and uranium). The soil conditions in different regions are not the same, and the hydrological conditions are also very different, which has a great impact on the formation and stability of colloids. Bentonite can produce colloids due to the erosion of groundwater, and the interaction between radioactive nuclides and bentonite colloids can affect the release of nuclides into the environment. The colloidal behavior of plutonium in the bentonite groundwater system was studied under anaerobic conditions, and the particle size distribution of plutonium colloids was measured. The effects of pH (6.0-10.0) and ion strength (0.10-0.3 mol/L) on the colloidal stability and particle size of plutonium in the Beishan groundwater-bentonite system were obtained, and the interaction between plutonium and bentonite colloids was preliminarily explored. The experimental results show that pH has little effect on the particle size and Zeta potential of plutonium colloids and bentonite colloids. The increase of ion strength has little effect on the Zeta potential, but it accelerates the aggregation of colloids. The migration behavior of plutonium depends on the colloidal behavior of GMZ bentonite. In this experiment, approximately 85% of plutonium is adsorbed on bentonite colloids, and the presence of bentonite colloids is not conducive to inhibiting the migration of plutonium.