To　reduce　the　volumetric　mixing　rate　of　the　integrated　energy　recovery-pressure　boost　device,　a　novel　symmetrical　duct　structure　with　diversion　surface　was　proposed.　The　surrogate　model-based　multi-objective　optimization　framework　was　established,　and　obtained　the　optimal　ducts　V1　and　V2　combined　with　computational　fluid　dynamics　simulation.　Numerical　results　indicate　that　optimized　duct　structure　could　promote　the　formation　of　plug　flow　and　effectively　improve　the　collision　efficiency　between　high-pressure　brine　and　low-pressure　seawater,　and　the　volumetric　mixing　rate　corresponding　to　the　ducts　V1　and　V2　was　reduced　by　31.52%　and　22.18%,　and　the　duct　volume　efficiency　was　increased　by　16.04%　and　19.56%,　respectively.　Finally,　the　performance　of　optimized　device　was　verified　through　seawater　reverse　osmosis　desalination　system　under　actual　working　conditions.　Experimental　results　showed　that　the　mixing　rate　of　optimized　ducts　had　a　significant　decrease　of　30.86%　and　20.53%　in　the　applicable　range,　and　the　energy　recovery　efficiency　improved　at　most　5.41%　and　7.55%,　respectively.　The　optimized　ducts　could　significantly　reduce　the　specific　energy　consumption　of　the　desalination　system　by　26.01%　and　18.22%,　respectively,　and　the　specific　energy　consumption　reached　the　lowest　level　of　3.02　kWh/m3,　demonstrating　the　superiority　of　the　structure　and　the　accuracy　and　effectiveness　of　the　optimization　strategy.