Rotary　energy　recovery　devices　(RERDs)　play　a　significant　role　in　reducing　the　consumption　of　energy　used　in　the　desalination　of　seawater　by　reverse　osmosis　(SWRO).　An　integrated　energy　recovery　and　pressure　boost　device　(IERPBD)　applied　to　the　recovery　of　hydraulic　energy　from　the　concentrated　brine　and　pressurizes　synchronously　the　seawater　is　introduced.　To　address　the　complex　motion　of　the　multiple　lubricating　gaps　in　IERPBD,　especially　piston　ball/slipper　and　slipper/swashplate　interfaces,　an　innovative　computational　fluid　dynamics　(CFD)　model　based　on　User　Defined　Function　(UDF)　is　originally　proposed.　The　characteristics　of　pressure,　flow　and　mixing　are　analyzed　to　reveal　the　influence　of　multiple　lubricating　gaps　leakage　and　mixing　on　energy　recovery　process.　In　addition,　a　SWRO　system　is　built　to　investigate　the　effect　of　operating　parameters　and　seawater　salinities　on　the　energy　recovery　and　mixing　properties　of　the　IERPBD,　and　its　structural　parameters　are　optimized　by　parametric　study,　which　further　reveals　the　comprehensive　characteristics　of　the　IERPBD.　The　results　indicate　that　the　proposed　CFD　methodology　can　precisely　analyze　the　energy　loss　and　mixing　properties　of　RERDs,　and　the　utilization　of　IERPBD　can　diminish　25.7%　of　the　energy　consumption　of　SWRO　system　with　24.2%　freshwater　recovery　ratio　and　10　m(3)/d　freshwater　production.