In　view　of　the　growing　need　for　water　hydraulic　actuators　in　underwater　operations,　a　scheme　was　propounded　to　develop　high　performance　water　hydraulic　axial　piston　motor　for　underwater　rotary　tools.　In　the　water　hydraulic　system,　the　water　hydraulic　motor　is　the　device　that　converts　the　pressure　energy　of　water　into　rotating　mechanical　one　to　drive　working　mechanisms.　Based　on　physicochemical　properties　of　water　and　the　working　principle　of　axial　piston　motor,　a　physical　model　was　developed,　numerical　and　experimental　studies　were　carried　out　to　research　its　output　performance,　including　the　output　torque,　rotating　speed　and　ripple.　The　results　prove　that　the　physical　model　is　reasonable,　and　show　the　effects　of　the　input　pressure　difference　and　the　flow　on　the　motor＇s　output　characteristics,　which　provide　a　basis　for　the　development　and　improvement　of　the　hydraulic　motor.　©　2018,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.