Abstract: The mechanism study is performed based on indoor geotechnical experiment by injecting acetic acid and carbonic acid with different concentrasion to soil samples and according to the results of the soil mechanics and the correlative theory.The conclusions are that by changing thickness of electric double layer of soil grain diffusion and adsorbability of polar water molecular, the concentration of acetate or carbonic acid makes soil particles ag-glomerate or disperse, and result in variation of plasticity and permeability of the compacted clay;By dissolving aluminium in clay mineral, acetic acid increases the clay permeability and plasticity index;There is a chemical re-action of the carbonic acid with the metal cation which can generate insoluble carbonates, resulting in decrease of the clay liner permeability.It gives evidences for the clay liner stability.