Seawater axial piston pump is a critical power component in seawater fluid power system. As the properties of high bulk modulus and low viscosity of seawater, the pressure and vibration characteristics of the seawater axial piston pump will be getting poorer than the traditional oil pump. In this study, the pressure, flow, and vibration characteristics for a seawater axial piston pump are investigated. The three-dimensional computational fluid dynamics simulations for the port plate with non-grooved, U-shaped, and triangle-based pyramid silencing groove designs have been conducted over a range of operating conditions, which consider the fluid compressibility effect and cavitation damage. Measurements of pressure ripple and pump vibration are carried out at various loading conditions to verify the results of simulation. The experiment turned out that the well-designed port plate can mitigate both pressure ripples as well as vibrations of the pump. This research will lay the foundation for the further development of a low fluid noise seawater axial piston pump.