Abstract: The permeability of liner, which determines the effectiveness of landfill, is influenced considerably by leachate and pressure condition. In light of the actual leachate and pressure state of landfill liner, the effect of simulated leachate concentration and vertical pressure on the hydraulic conductivity of compacted clay liner is studied. When water is substituted by simulated leachate, which, in this case, is CaCl2 solution, the hydraulic conductivity increases three times at the most； while when vertical pressure doubles from 200kPa to 400kPa, the hydraulic conductivity reduces about an order of magnitude. Compression and consolidation tests and dual-factor variance analysis confirm that the hydraulic conductivity is remarkably affected by vertical pressure compared with simulated leachate. It is suggested that the effect of vertical pressure on hydraulic conductivity should be taken into account in the design and assessment of liners.