To　investigate　the　flow　characteristics　of　the　water　hydraulic　axial　piston　pump,　the　mathematical　model　of　the　flow　distribution　characteristic　of　the　port　plate　was　established　in　this　study,　which　considers　the　pre-compression　angle　of　the　port　plate,　the　leakage　flow　through　the　piston/cylinder　gap　and　the　port　plate/valve　plate　gap.　The　structure　parameters　of　the　port　plate　were　optimally　calculated.　The　dynamic　simulation　on　the　flow　field　of　the　water　hydraulic　axial　piston　pump　with　different　sizes　of　pre-compression　angle　were　implemented　using　PumpLinx　software,　and　the　influences　on　the　properties　of　flow　distribution　for　each　size　of　pre-compression　angle　were　investigated.　Simulation　results　show　that　the　fluid　in　the　discharge　chamber　can　flow　into　the　piston　chamber　reversely　during　the　pump　working　in　the　discharge　period.　The　rate　of　reverse　flow　in　the　piston　chamber　directly　relates　to　the　flow　ripples　and　pressure　ripples　of　the　pump.　When　the　pre-compression　angle　is　improved,　the　reverse　flow,　flow　ripple　and　pressure　pulsation　in　the　piston　chamber　can　be　reduced,　therefore,　the　flow　characteristics　of　the　pump　increase.　When　the　pre-compression　angle　is　set　to　be　20°,　the　best　result　can　be　obtained.　If　the　pre-compression　angle　exceeds　20°,　a　higher　flow　ripple　is　obtained　because　of　the　superposition　of　the　reverse　flow.　©,　2015,　Beijing　University　of　Technology.　All　right　reserved.