This paper provides a detailed analysis of the abnormal vibration issues of the butterfly valve in the intake of the water turbine of Unit 8 at a certain power plant under different load conditions. Field tests were conducted to collect vibration, pressure pulsation, and noise data from the butterfly valve across a load range from no load to full load (150 MW). The study reveals that the abnormal vibrations of the butterfly valve are particularly noticeable when the load exceeds 135 MW, with significant increases in vibration amplitude, and the vibration frequency closely matches the valve’s natural frequency. Preliminary analysis suggests that this phenomenon results from resonance induced by the Kármán vortex street. To resolve this issue, a structural modification plan for the butterfly valve is proposed, including reworking the downstream end of the reinforcement ribs on the butterfly valve disc to increase the vortex street frequency and eliminate the resonance. Experimental results show that the vibration amplitude of the modified butterfly valve is significantly reduced, and the unit has returned to stable operation. Finally, the paper summarizes the experience of effectively suppressing resonance through structural modifications, providing useful references for similar engineering projects.