Water　hydraulics　have　board,　promising　application　and　development　prospects　in　ocean　exploration,　marine　resources　exploitation,　and　other　fields　because　of　its　superiorities　underwater.　Underwater　manipulator　is　an　important　equipment　to　perform　underwater　tasks.　By　integrating　water　hydraulic　transmission　and　the　underwater　manipulator,　the　complexity　of　the　underwater　vehicle-manipulator　system　can　be　reduced,　and　the　functionality　can　be　uplifted.　By　expounding　the　structural　characteristics,　research　progress　and　commercialization　status,　the　pros　and　cons　of　different　driving　power　and　its　influence　toward　the　performance　and　design　point　of　manipulators　are　detailed　which　come　the　conclusion　that　water　hydraulic　transmission　is　the　optimal　solution　for　underwater　tools.　As　key　technical　issues　that　need　to　be　solved　in　the　design　of　water　hydraulic　manipulator,　the　research　progress　of　tribology　and　lubrication,　materials,　dynamics　modelling,　and　motional　control　are　analysed　and　summarized.　Finally,　the　development　trend　of　underwater　manipulator　is　prospected,　and　the　conclusion　is　given　to　provide　a　reference　for　relevant　research.　©　2023　Editorial　Office　of　Chinese　Journal　of　Mechanical　Engineering.　All　rights　reserved.