Energy　recovery　device　(ERD)　is　a　critical　power　component　in　seawater　reverse　osmosis　(SWRO)　desalination　system.　In　this　study,　the　energy　transfer　and　flow　characteristics　for　an　innovative　integrated　energy　recovery　and　pressure　boost　device　(IERPBD)　are　investigated.　The　IERPBD　which　consists　of　a　rotary　pressure　exchanger　(RPE)　and　an　axial　piston　type　booster　pump　(APBP)　is　introduced　in　Section　2.　To　optimize　both　the　structure　parameters　and　working　conditions　of　IERPBD,　a　series　of　three-dimensional　(3D)　CFD　simulations　are　carried　out.　The　CFD　simulations　for　the　RPE　with　port　plate　silencing　grooves　are　conducted　with　a　set　of　operating　conditions　through　orthogonal　designed　theory.　It　should　be　noted　that　the　leakage　through　the　lubricating　gaps　of　valve-port　plate,　fluid　compressibility　effect　and　cavitation　damage　are　considered　in　the　simulation.　And　partial　numerical　results　are　validated　by　comparison　with　the　results　from　other　research　groups.　The　mixing　process,　pressure　distribution,　components　distribution,　leakage　flow　characteristics　and　related　characteristic　parameters　of　RPE　are　presented　in　Section　3.　And　then　the　optimal　parameters　of　RPE　with　a　duct　diameter　of　10　mm,　duct　length　of　70　mm,　12　ducts　with　fresh　seawater　flow　of　10.8　L/min　were　used　to　design　the　IERPBD.　The　energy　transfer　and　flow　characteristics　of　IERPBD　were　also　presented　with　different　gap　heights　of　the　valve-port　plate　interface.　The　simulation　results　turned　out　that　when　the　lubricating　gap　height　of　valve-port　plate　changes　from　5　mu　m　to　20　mu　m,　the　flow　ripple　rate　of　RPE　could　increase　from　6.15%　to　36.13%,　whereas　the　energy　recovery　efficiency　of　RPE　could　decrease　from　97.2%　to　49.8%.　Therefore,　a　well-designed　lubricating　gap　of　valve-port　plate　could　improve　both　energy　transfer　and　flow　characteristics　of　IERPBD.　This　research　will　lay　the　foundation　for　the　further　development　of　high　efficiency　and　low　fluid　noise　IERPBD.