Abstract: To address the severe noise issue caused by insufficient oil suction in gear pumps at high rotational speeds and clarify the influence mechanism of a front-mounted boosted centrifugal pump on the noise characteristics of gear pumps, a high-speed gear pump noise test rig was first established. Tests show that the vibration and noise of the gear pump vary nonlinearly under different flow rates supplied by the centrifugal pump. Furthermore, based on CFD and Lighthill acoustic analogy theory, a coupled sound-flow field model of a gear pump in series with a centrifugal pump was developed, and numerical simulations were conducted to analyze turbulent noise, trapped-oil noise, flow ripple noise and cavitation noise. The results indicate that the volumetric efficiency of the gear pump first increases and then tends to be stable with the rise of the flow rate supplied by the centrifugal pump, while the vibration and noise first increase and then decrease. A critical point of flow ratio exists in this process, that is, the flow rate supplied by the centrifugal pump is 1.2 times that of the gear pump (QC/QG=1.2).Before the critical point, the volumetric efficiency increases with the supplied flow rate, with a maximum increase of 8.68% compared with the standalone gear pump. In this stage, the fundamental-frequency sound pressure level at the inlet and outlet decreases due to the decline of gas volume fraction, accompanied by the increase of bulk modulus and the recovery of oil stiffness, which improves the transmission efficiency of the fluid as an acoustic propagation medium, while the bubble damping effect decreases and shows an upward trend. Beyond the critical point, the volumetric efficiency remains nearly unchanged, and the sound pressure level drops due to the weakened noise induced by cavitation, oil trapping and flow ripple. Meanwhile, the turbulent kinetic energy and oil stiffness cease to intensify and show a downward trend. Among the causes for the reduction of sound pressure level, the decrease of cavitation intensity is the dominant factor, accounting for 60.91%, whereas the effect of trapped-oil pressure is minimal and negligible. This study provides a theoretical basis and design guidance for achieving high volumetric efficiency and low noise in gear pumps at high rotational speeds