The paper considers the problem of modernizing the runner of a high-head Francis turbine for the specified parameters. The modernized runner must meet modern requirements for efficiency and cavitation. Using a package of application programs, a blade system of the runner was developed for the accepted parameters of the optimal mode with high energy-cavitation performance. The results of the computational analysis of flow parameters in the flow space of the high-head hydro turbine Fr310 of increased speed are presented. Constantly growing requirements for improving the energy qualities of hydraulic turbines necessitate the improvement of methods that allow predicting and optimizing the energy characteristics of the flow space. Improving the energy-cavitation performance of hydraulic turbines poses the task of further developing the method of mathematical modeling of the workflow. The use of a numerical experiment based on a mathematical model of the workflow is an effective means of finding rational options for both newly designed and modified elements of the flow space of hydraulic turbines. A necessary component of the design of the flow part is the selection of a number of geometric parameters of the runner (meridional outlines of the cavity, input and output edges of the blade, etc.), the correctness of which significantly affects the energy performance. When choosing the geometric parameters of an runner, one is usually guided by experimental data obtained for hydraulic turbines depending on the speed. This approach does not ensure proper coordination of the geometric parameters of the runner, which often results in both a discrepancy between the design mode and the optimal one and an insufficiently high level of energy performance.