It　is　well　established　that　clays　can　exhibit　semipermeable　membrane　behavior　and　osmotic　efficiency　is　used　to　describe　the　membrane　behavior　of　clays.　Several　experimental　results　have　already　verified　that　osmotic　efficiency　is　not　constant　when　pore-fluid　chemistry　changes.　In　this　article,　based　on　the　mechanical　balance,　generalized　Darcy＇s　law　and　the　principle　of　mass　conservation,　an　improved　fully　coupled　hydro-chemo-mechanical　model　is　proposed　for　saturated　clayey　materials,　in　which　osmotic　efficiency　is　treated　as　a　variable　that　depends　on　the　solute　concentration,　grain　density,　porosity　of　soil,　and　cation　exchange　capacity.　Numerical　simulations　are　conducted　to　investigate　the　influence　of　variable　osmotic　efficiency　on　solute　transport.　The　results　show　that　solute　transport　is　very　sensitive　to　osmotic　efficiency　and　when　the　transport　time　is　10　years,　the　difference　in　influence　depth　reaches　about　13.6　cm　with　constant　(0.069)　and　variable　(initially　0.069)　osmotic　efficiencies,　this　indicates　that　semipermeable　membrane　behavior　of　clays　with　variable　osmotic　efficiency　restricts　the　solute　transport　effectively　and　slows　down　the　solute　movement　strongly.　The　difference　in　breakthrough　time　reaches　15.8　years　with　osmotic　efficiency　(0.069).　The　proposed　coupled　model　can　be　used　to　guide　the　design　of　clay　liners　and　evaluate　their　service　performance.