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To explore the hydraulic performance of the impact water turbine of JP75 hose reel irrigation machine, experimental investigations were conducted by replacing the load of the machine with the baking torque of an eddy-current brake. The internal flow characteristics of the turbine were also investigated numerically based on the SST k-ω turbulence model. On this basis, orthogonal numerical experiments were made to determine the main factors affecting the hydraulic performance of the turbine. The results showed that the power and head loss of the turbine were increased as a parabola with the increase of the flow rates, but the maximum efficiency of the turbine under different conditions was less than 35%. A recirculation zone was found downstream of the inlet nozzle exit, which reduced jet velocity of the nozzle, resulting in the reduction of torque produced by the turbine. The flows out of the nozzle passed the impeller mainly through a mainstream impeller passage, and the pressure on the pressure side of the blade in the mainstream passage was higher than pressure in other areas of the impeller. The flow velocity in the annular channel downstream the trailing edge of the blades was relatively high, which blocked the flow inside the impeller and resulted in the recirculation in the impeller passages. The diameter of nozzle orifice and the blade tip clearance had significant influence on the hydraulic performance of the water turbine. An improved water turbine, with a novel nozzle and appropriate blade cutting and axial impeller-casing clearance was obtained based on the numerical orthogonal tests. The best efficiency of 52.21% was achieved for the modified model optimized by numerical orthogonal experiments. Compared with the original model, the modified model showed a significant overall reduction in head loss (20%~30%), an improvement in output power (10%~15%) and an efficiency increment of 12~17 percentage points under different operating conditions.