The　membrane　efficiency　coefficient　is　a　critical　theoretical　indicator　used　to　assess　the　performance　of　clay　barriers　in　landfills.　At　present,　the　membrane　efficiency　coefficient　is　determined　in　response　to　a　single　ion,　which　cannot　be　used　to　accurately　evaluate　the　performance　of　clay　barriers　under　multiionic　leachates.　Therefore,　a　membrane　efficiency　model　must　be　developed　considering　multiionic　conditions.　In　this　study,　a　membrane　efficiency　model　of　clay　under　multiionic　conditions　is　established　based　on　the　mineral-pore　fluid　interactions　and　triple-layer　model.　The　proposed　model　is　validated　by　comparing　the　predicted　and　measured　results　of　the　variation　in　membrane　efficiency　coefficients　with　mixing　ratios　under　multiionic　conditions.　Results　indicate　the　proposed　model　accurately　determines　the　membrane　efficiency　of　clay　under　multiionic　conditions.　The　predicted　membrane　efficiency　coefficient　decreases　with　increasing　solution　concentration　and　void　ratio　due　to　the　weakened　mineral-pore　fluid　interaction.　The　proposed　membrane　efficiency　model　can　provide　a　more　accurate　theoretical　tool　to　assess　the　performance　of　clay　barriers.