Abstract: In the waste filling, it is extremely important that the earthfill retards the percolation of the waste leached solution. On the basis of a large number of test data, the paper presents the decontamination mechanism and laws of ions frequently appearing in leachate. The results of earthcolumn tests indicate that the structure of layers has effects on the transporting and cleaning of ions in different degree with different ions; that due to exchange of adsorption with bivalent cation (Ca 2+ ,Mg 2+ )in place of monovalent ions the permeability increases 5～10 times; that potential function of typical monovalent ions (NH 4 +,Cl -) is exponential.