A　water　hydraulic　flexible　gripper　with　three-fingered　structure　is　developed　to　deal　with　the　problem　of　poor　adaptability　for　the　existing　underwater　gripper.　This　gripper　driven　by　water　hydraulics　can　realize　flexible　grasping　and　possess　simple　structure,　high　pressure-bearing,　strong　adaptability　and　capability　of　anti-jamming　to　the　water　environment　and　easy　to　control.　In　particular,　the　water　hydraulic　flexible　gripper　system　is　an　open　system　in　relation　to　the　underwater　environment,　with　the　water　source　being　supplied　directly　by　the　underwater　environment,　eliminating　the　effects　of　back　pressure　generated　by　the　underwater　environment　in　comparison　with　the　closed　system　of　other　grippers.　It　is　a　good　solution　to　solve　the　problem　of　poor　adaptability　for　the　existing　underwater　gripper　in　underwater　environment.　The　flexible　actuator　model　is　established　to　explore　the　key　parameters　influencing　the　deformation　characteristics.　The　effects　of　different　inlet　pressure,　knuckle　length,　wall　thickness　and　material　of　the　inner　skeleton　and　external　surface　on　the　deformation　characteristics　of　the　flexible　actuator　are　investigated　through　simulation.　It　is　found　that,　for　the　flexible　actuator,　the　wall　thickness　of　the　inner　skeleton　is　selected　as　1　mm　and　the　inner　skeleton　length　is　designed　with　the　first　knuckle　of　30　mm　and　the　second　knuckle　of　80　mm.　Based　on　the　optimal　parameters　obtained　through　simulation,　the　prototype　of　flexible　actuator　and　flexible　gripper　are　fabricated.　Experiment　is　performed　to　test　the　deformation　of　the　flexible　actuator　under　different　inlet　pressure.　It　is　found　that　the　experiment　results　are　consistent　with　the　simulation　results.　Both　of　the　experiment　and　simulation　results　exhibit　that　the　total　deformation　of　the　flexible　actuator　is　proportional　to　the　inlet　pressure.　The　research　will　lay　foundation　for　the　optimal　design　of　flexible　actuator　used　for　the　underwater　gripper　driven　by　water　hydraulics.