Noise reduction in pumpjet propulsors (PJPs) is crucial for improving the stealth capabilities of high-performance underwater vehicles. This study designs a serrated trailing edge for the stator of PJPs to reduce their radiation noise, whose performance is comprehensively evaluated via computational modeling. The improved delayed detached eddy simulation model is used to simulate the transient flow inside the PJP and obtain the fluctuating pressure on its surface, based on which the FW-H analogy is applied to perform acoustic integration, generating noise data of the PJP. Additionally, the acoustic and flow field data before and after the modification are compared to verify the effect of the serrated stator trailing edge on noise reduction of PJP. The results show that designing the serrated trailing edge at 6% chord length of the stator did not significantly affect the PJP’s hydrodynamic performance. Moreover, the serration design demonstrated the most effective noise reduction at high advance coefficients of the PJP, particularly in reducing radial radiation noise (at least by 2 dB) and low-frequency noise (below 2500 Hz). Our research provides a feasible resolution for noise reduction of rotating machinery.