Abstract: This study aims to investigate the influence of stress and chemical solution on the hydraulic conductivity of Geosynthetic Clay Liner (GCL) using flexible wall permeation tests. The results indicate that the hydraulic conductivity of GCL exhibits an excellent linear relationship with pressure on a logarithmic scale under distilled water. However, the expansion of bentonite particles in GCL is inhibited by a chemical solution, which increases the pore size, porosity, and hydraulic conductivity of GCL. The hydraulic conductivity of GCL is primally related to the concentration and cation valence of the chemical solution. When the concentration increased from the same value (0.01 to 0.20 mol/L), the hydraulic conductivity under the CaCl2 solution increased from 4.12×10-11 to 4.22×10-7 m/s (up to four orders of magnitude) while under the NaCl solution only changes from 5.32×10-11 to 7.00×10-11 m/ s, which indicates that the influence of divalent cation on the hydraulic conductivity of GCL is significantly higher than that of the monovalent cation. Meanwhile, the hydraulic conductivity of GCL with uneven particle distribution by disturbance cannot meet the China standard (<5.0×10-11 m/s). Under the coupling effect of the chemical and stress, when the stress increase from 50 to 250 kPa, the hydraulic conductivity of GCL decreases to less than 5.0×10-11 m/s under the low concentration or monovalent cationic solution. In contrast, under the high concentration and valence cation solution, the hydraulic conductivity of GCL decreased from 4.22×10-7 to 2.87×10-10 m/s (about three orders of magnitude). However, 2.87×10-10 m/s still cannot meet the requirements of the China standard. The concentration and type of the solution and the montmorillonite content on the micro-scale affect the expansion of a bentonite particle. However, the mesoscale particle size, particle distribution, porosity, and pore size, are crucial in determining the structural evolution of GCL and the hydraulic conductivity.