In order to research the internal sound field characteristics and reduce the running noise of self-priming vortex pump at low-flow rate, the CFD and Lighthill sound analogy theory was adopted to solve the internal acoustic field and optimize the noise of self-priming vortex pump. Firstly, the pressure fluctuation of self-priming vortex at 0.4Qd，0.8Qd and Qd were obtained from the unsteady simulation with the RNG k-ε turbulence model in CFX software. The datum of pressure fluctuation were extracted and input into the ACTRAN acoustics software, the SPL of the pump discharge, internal sound pressure distribution and main noise source in pumps at different flows were got by acoustic field calculation. Then，according to the laws of the Ewald frequency modulation, four different types of unequal spacing impellers were designed with modulation angle A of 2°, 4°，6°and 8°. Finally, the acoustic field calculation of four different impellers was conducted, the impeller with unequal spacing and A value of 4°had lower noise, whose sample made by 3D printing was chosen to conduct the performance and noise reduction test. The simulation results showed that the flow-induced noise of self-priming vortex pump was closely related to the pressure fluctuation which mainly caused by rotor-stator interaction，both of them had the same frequency characteristic，the maximum sound pressure appears at two times blade passing frequency. With the decrease of the flow rate, the SPL of the pump discharge was increased, the sound source of the self-priming vortex pump was mainly distributed in the channel and the tongue close to the pump discharge. The noise test results showed that the impeller sample with A value of 4°had little effect on the performance of the self-priming vortex pump and can reduce noise at low-flow rate, under the design point, noise can be decreased by 4dB, and it can be decreased by 2dB when low flow was 0.4Qd.