Abstract: In order to reveal the transient characteristics of water-jet pump with different diffuser numbers, the flow field and sound field of water-jet pump were carried out based on DES hybrid simulation and FEM acoustic finite element method. The accuracy of numerical computation method on transient characteristics was verified by the experimental results. The influence of different diffuser blade numbers（Z=5,6,7） on the thrust, pressure pulsation and flow-induced noise of water-jet pump were studied. The results show that with the increase of diffuser blade number, the thrust first decreases and then increases, but the flow rate gradually decreases, and the torque gradually increases. The diffuser blade number has a relatively small influence on the distribution pattern of pressure pulsation at the impeller outlet, but has a significant influence on the pressure pulsation amplitude at the main frequency. The pressure pulsation amplitude at the hub decreases first and then increases with the increase of diffuser blade numbers, while the amplitude at the rim and flow passage center gradually decreases with the number of diffuser blade increasing. The diffuser blade number affects the main frequency distribution of the flow-induced noise, and the increase of the diffuser blade number is beneficial for reducing the amplitude and total sound pressure level at the main frequency of the flow-induced noise in the water-jet pumps.