Abstract: Vortex rope in the draft tube of a Francis turbine is a key factor causing vibrations of the turbine unit. To reduce the vibrations, unsteady 3D flows in a Francis turbine were numerically simulated in this work to investigate amplitude and frequency characteristics of the pressure fluctuations in the draft tube. Three improving measures were examined: extending the runner cone, adding a hydraulic disturbance of 0.03Q to the flow rate, and combining these two modifications. Simulations of all these different cases were analyzed and compared, focusing on their effects on the vortex rope-generated pressure fluctuations. The results show that all the three measures can effectively reduce the fluctuations. A longer runner cone has an obvious effect on pressure fluctuations in the conical tube. Compared to disturbing the flow rate, a longer cone or the combination measure is more effective in frequency modification and amplitude reduction of the draft tube fluctuations, but their influences on turbine efficiency are greater.