In　the　field　of　marine　research,　the　soft　actuator　has　a　better　flexible　grasping　effect　and　adaptability　to　the　target　object　compared　with　the　traditional　rigid　manipulator.　In　this　paper,　a　soft　actuator　based　on　water-hydraulic　technology　is　proposed.　The　material　parameters　of　the　Yeoh　3rd-order　model　is　determined　based　on　uniaxial　testing,　and　a　mathematical　model　of　the　input　pressure　and　deformation　of　the　water-hydraulic　soft　actuator　(WHSA)　is　established.　The　optimal　structural　parameters　of　the　rectangular　chamber　WHSA　are　selected　by　orthogonal　test.　The　bending　deformation　of　WHSA　under　different　pressure　conditions　is　simulated　with　thermoplastic　polyurethane　(TPU)　as　the　material.　The　deformation　of　WHSA　under　different　pressure　is　measured　experimentally　to　verify　the　consistency　of　the　simulation　and　theoretical　results　and　the　rationality　of　the　design.　Meanwhile,　the　pressure-holding　experiment　and　grasping　experiment　of　WHSA　are　conducted,　which　confirmed　the　important　application　value　and　application　potential　of　WHSA　in　the　underwater　manipulator　with　better　flexibility　and　adaptability　in　comparison　with　traditional　rigid　manipulators.