Abstract: Hydrodynamic turbines as a mature and reliable method for energy recovery have a broad range of applications. Compared to developing specialized hydrodynamic turbines for energy recovery, using pump reversal as a turbine is more cost-effective. This study employs CFX numerical simulation to analyze internal flow and hydraulic loss of a six-stage guide vane multistage centrifugal pump operating in turbine mode. The findings indicate: that the shaft power and head of the multistage pump increase with the flow rate rising. At the same time, the increase rate rises. During turbine operation, fluid pressure decreases progressively from the inlet to the outlet, with the impeller being the high-velocity region and the guide vane transition zone exhibiting the lowest velocity. As the flow rate increases, the vortex regions within the impeller and guide vanes decrease, with a more pronounced reduction in the impeller region.After the fluid passes through the final impeller stage into the turbine casing, two distinct vortex bands form on either side of the guide vanes. With flow rate increasing, the distribution of these vortex bands evolves from disordered to symmetrical and eventually to an asymmetrical state, extending towards the outlet extension during this process.When functioning as a turbine, hydraulic losses increase with flow rate rising, and impellers and guide vanes accounting for the largest proportion of these losses, and the rate of loss increase in guide vanes exceeds that in impellers.