Underflow dissipation floodgates are subjected to severe pier vibrations during high-flow discharge. Addressing to this issue, the hydraulic elasticity model test and prototype observation of a hydropower station were conducted, with which two vibration reduction measures of improving pier structure and optimizing reservoir regulation schemes were proposed. The model test provided data support for the analysis of pier vibrations, while the prototype observation validated the reliability of the model test. When the discharge flow is 5 400 m3/s, the combined discharge approach of “low orifices and surface orifices” can reduce the flow through surface orifices from 5 400 m3/s in standalone discharge to 1 919 m3/s in combined discharge, and the rest 3 481 m3/s can discharge from the low orifices. In this case, the standard deviation of pier vibration displacement at surface orifices decreases from 182.3 to 51.7 μm, achieving a vibration reduction effect of 71.6%. When the discharge from the surface orifices reaches 10 030 m3/s, reinforcing the piers can reduce the standard deviation of pier vibration displacement from 288.8 to 129.6 μm, leading to a vibration reduction effect of 55.1%.