Employing　hydrogels　as　a　substitute　for　cement　in　soil　stabilization　is　believed　to　have　great　environmental　benefits.　However,　current　hydrogel　soil　stabilizers　cannot　function　properly　in　wet　conditions　due　to　swelling-induced　structural　deformation　and　mechanical　weakening,　which　significantly　limits　their　applications.　To　overcome　current　technical　limitations　and　achieve　sustainable　cement-free　soil　stabilization,　we　developed　a　water-resistant　hydrogel　soil　stabilizer　that　worked　under　both　dry　and　wet　conditions　inspired　by　the　mussel　byssal.　Carefully　formulated　precursors　containing　methacrylic　acid　and　acrylamide　were　poured　into　soils　and　cured　via　in-site　polymerization.　The　synergic　effect　of　intermolecular　hydrogen　bonding　and　hydrophobic　interactions　led　to　the　formation　of　heterogeneous　mussel　mimicry　microstructures　that　possessed　superior　toughness　(up　to　2.1　MJ/m3)　and　ultra-low　swelling　ratios.　Soils　strengthened　with　such　hydrogels　maintained　great　strength　(up　to　2.9　MPa)　in　both　air　and　water,　which　had　never　been　achieved　before.　The　intrinsic　water　affinity　of　hydrogels　also　ensured　a　decent　permeability　and　retention　ability　of　water,　which　was　critical　to　the　ecosystems.　In　conclusion,　a　tough,　water-resistant,　and　multi-functional　mussel　mimicry　hydrogel　has　been　devised.　It　holds　great　promise　as　the　next-generation　cement-free,　ecofriendly,　and　sustainable　soil　stabilizers.