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Optimization of the structure parameters for the impulse water turbine of a JP75 hose reel irrigator was presented with the aim to improve the hydraulic performance of the turbine. The SST k-ω turbulence model was adopted to analyze the flow field characteristics and the hydraulic performance of the water turbine. The reliability of the numerical method was verified by the available experimental data. On this basis, single factor experiments were conducted numerically to investigate the influence of the structure parameters on efficiency, driving torque and pressure drop of the turbine. Taking the impeller axial clearance width (axial clearance), the roundness radius of the outlet pipe entrance (roundness radius) and the spacing of the impeller axis and nozzle center line (center spacing) as the influence factors, three factors and three levels of quadratic regression orthogonal numerical testes were carried out by using Box-Benhnken central composite experimental design principles. Subsequently, the response surface methodology (RSM) was employed to analyze the influence of various factors on the efficiency, driving torque and pressure drop of the turbine under the design conditions. The results showed that the established quadratic pdynomial respense surface model is accurate enough to represent the corresponding relationship between the design variables and the response indicators. The spacing between impeller axis and nozzle center was the most important factor affecting the hydraulic performance of the water turbine. The optimal parameters combination of center spacing of 73mm, axial clearance of 2mm and roundness radius of 20mm was obtained by using optimization module of Design-Expert data analysis software. The hydraulic performances of the optimized water turbine were predicted by using the proposed numerical simulation method and measured on a test rig. Compared with the original water turbine at the nominal operation point, the efficiency of the optimized turbine was increased by 17.6 percentage points, the torque was augmented by 13.2%, and the pressure drop was reduced by 29.3%.