Abstract: Recently,geosynthetic clay liners(GCLs) have been more and more used in different anti-seepage engineering projects.Their anti-seepage availabilities include hydraulic properties,absorption ability and internal shear strength and GCLs become a focus of designers and researchers.Swelling characteristics and hydraulic properties of GCLs under vertical stress were studied through hydration swelling tests and permeation tests.It was indicated that:(1) swelling of GCLs decreased with the increasing of vertical stress,but the hydraulic conductivity of GCLs decreased at the beginning,and then increased a little;(2) hydration-loading sequence had impact on both swell and hydraulic conductivity of GCLs;(3) in practice,GCLs had better been fully hydrated before loading on them,thus the anti-seepage availability could be greatly improved.