Regarding the local flow field and sediment changes caused by the underwater placement of continuous structures, the RNG k-ε turbulence model was used to establish an underwater sediment erosion and deposition model for elevated continuous structures, simulating the flow field and sediment migration changes near the pile foundation. The results indicate that the sediment on the upstream side of the pile foundation experiences scouring due to the shear effect of vortices, with the maximum depth of the scour hole occurring before the upstream pile foundation, forming a 45° angle with the flow direction and symmetrically distributed along the pile foundation axis. While the outflow side generates trailing vortices, significantly reducing flow velocity and resulting in minor sediment deposition. When the structure is long and intersects with the longitudinal boundary, the upstream flow can only rise or dive, leading to a sharp increase in flow velocity beneath the structure, intensifying the scouring effect, and forming a zigzag-shaped scour hole between the pile foundation and the side wall. The shear force and shear velocity at the seabed initially increase and then decrease, eventually tending towards equilibrium. At the balance of erosion and deposition, both shear force and shear velocity are positively correlated with the scour depth. Without elevation, minor sediment deposition occurs at the top of the pipe gallery, and the elevation height does not affect the scouring situation of the front row of pile foundations, but the thickness of sediment deposition behind the pipe gallery is positively correlated with the elevation height of the pipe gallery. The analysis results can provide a reference for the placement of underwater elevated continuous structures.