In this work, experimental and theoretical methods were used to investigate the role of poly aluminum chloride on thallium removal in the liquid phase. Experimental results indicated that poly aluminum chloride mainly played the role of absorbent. Meanwhile, it exhibited a certain catalytic effect in the chemical precipitation process. Theoretical results indicated that the bridge site between two Cl atoms was easier to adsorb Tl+ and Tl3+. Al2(OH)4Cl2 and [Al2(OH)4Cl2]2 were conducive to the adsorption of Tl+ and Tl3+ respectively. Further-more, excessive Cl atoms were not conducive to the ad...