Abstract: Modifying runner crown profile is a common method of turbine retrofit design, and for optimization and technical reform of a water turbine, exploring the influence of its crown profile on hydraulic performance is very significant. For this purpose, a Francis model runner was selected in this work, and four schemes were examined to modify its crown profile. Then, a CFD method was used to simulate and compare different crown profile schemes in terms of internal flow behaviors, energy characteristics, cavitation performance, and discharge capacity of this runner in three working conditions: small flow, optimal operation, and large flow. The results show that an appropriate elevation of the crown increases the discharge capacity through raising the lowest pressure on the runner blades, and that in large flow cases, it also improves energy characteristics and cavitation performance. However, an excessive crown height, in small flow cases, would produce negative impacts on the location and intensity of those vortices in the blade channels. Compared with the original runner design, scheme 4 can increase efficiency by 0.33% and 0.67% in large and small flow cases respectively. In small flows, a higher crown moves the blade channel vortices toward the blade inlet edge and intensifies their strength, thus resulting in a greater hydraulic loss and lower efficiency of the runner. In large flows, elevating crown profile may lead to a backflow zone near the crown and at the runner blade inlet, and consequently to an uneven distribution of pressure on the blades. Our study also reveals that runner efficiency and its internal flow at optimal operation generally vary little under different elevation of the crown, while the internal flow is very sensitive to even a subtle change in the flow parameters of a practical water turbine remodeling project. Thus, in estimating the change in energy characteristics of a new runner, we cannot rely on any intuitive judgment but rather, we must be very careful and perform multiple checking in making choice based on CFD analysis. This is the way to ensure the hydraulic performance of the new runner, the only way to reduce to the lowest the risk in technical improvement of a Francis turbine. The conclusions above would be helpful for runner remodeling design and performance prediction of Francis turbines for hydropower stations.