CPTu　(piezocone　penetration　test)　is　widely　used　in　engineering　practice　to　determine　various　parameters　of　clays　under　partially　drained　conditions.　However,　most　existing　research　is　based　on　undrained　or　fully　drained　conditions　for　clays,　leading　to　underestimation　or　overestimation　of　soil　strength.　By　applying　the　Eulerian-Lagrangian　large　deformation　finite　element　method　to　analyse　the　water-soil　interaction,　the　CPTu　driving　mechanism　in　offshore　saturated　soft　clays　under　different　drainage　conditions　is　revealed.　An　advanced　hypoplastic　constitutive　model　for　clays　is　used　to　simulate　the　nonlinear　behaviour　of　kaolin　under　different　drainage　conditions.　The　generation,　accumulation,　and　dissipation　of　excess　pore　water　pressure　under　different　drainage　conditions　are　analysed,　as　well　as　the　influence　of　excess　pore　water　pressure　on　cone　tip　resistance　and　the　effective　stress　of　the　soil　during　the　CPTu　penetration　process.