Abstract: Updating the normal runner of a Francis turbine with certain long and short blades can produce significant changes in its energy performance, cavitation performance, and hydraulic stability. To apply this technique, full-passage numerical simulations of Francis turbines before and after the update have been conducted in this work to examine the three-dimensional cavitation turbulent flows and their unsteady behaviors in three typical conditions: small openings, rating conditions, and large openings. The results show that the efficiency of the updated turbine is increased by 6.7%, 6.2% and 6.8% in these three cases respectively and its cavitation performance improved significantly in the latter case. And the updating reduces pressure pulsation amplitude by 20.9% at small openings, 21.5% at rating conditions, and 13.8% at large openings (at monitoring point 1). Thus, the runner updating is effective in improving the performance of Francis turbines.