The　theory　of　two-dimensional　expression　in　the　tube　press,　where　a　semi-solid　material　is　compressed　on　a　cylindrical　filter　element,　is　investigated　under　constant　pressure.　An　equation　describing　the　two-dimensional　expression　process　is　derived,　based　on　Terzaghi＇s　model　in　soil　mechanics.　The　rate　of　two-dimensional　expression　is　affected　by　three　factors:　the　ratio　of　the　outer　to　the　inner　radius　of　the　original　material,　the　outer　radius　and　the　consolidation　coefficient　of　two-dimensional　expression.　Predictions　using　this　equation　are　shown　to　be　in　good　agreement　with　experimental　results　for　the　average　consolidation　ratio.