Abstract: To achieve green power supply and wireless operation for smart irrigation systems, pipeline hydropower generation is one of the technical means. Pipeline micro-hydro turbines have application potential in energy recovery from irrigation pipelines. However, the relationship between impeller parameters and hydraulic performance is complex and lacks systematic screening methods, making it difficult to balance power generation efficiency and hydraulic stability. Moreover, how blade angle adapted to different pipe diameters and responded to varying operating conditions—such as water-fertilizer solution density and terrain head—had not been well understood. To address these problems, this study proposed a precise optimization approach integrating transient–steady combined simulations and flow field visualization. First, 30 transient simulations with dynamic mesh technology were conducted to determine the rated speed range, followed by 66 steady-state simulations to evaluate power, head loss, and hydraulic efficiency. The optimal configuration was identified through flow field contour analysis and validated by power comparison tests on a simulated irrigation pipeline test platform under inlet pressures of 0.06–0.26 MPa. Using the optimized impeller, blade angle adaptability across 32, 90, and 110 mm pipe diameters was assessed based on geometric similarity criteria. Power output and flow field stability under different fertigation solution densities (1000–1200 kg/m³) and terrain height differences (4 m and 8 m) were then simulated and analyzed. Under baseline conditions, the impeller with 20 blades and a blade angle of 76° achieved the best overall performance, delivering the maximum output power and hydraulic efficiency while maintaining low head loss. Analysis of the internal flow field showed that this blade angle preserved a uniform velocity gradient, suppressed flow separation, and ensured stable flow paths. The pressure distribution was uniform, and the high-pressure zone was moderately intensified without causing severe impact losses. Streamline diagrams further confirmed that the flow closely followed the blade surfaces with negligible backflow. Physical experiments verified that the optimized design significantly outperformed a commonly used 24-blade commercial turbine over a wide range of inlet pressures. The optimal blade angle varied with pipe diameter due to differences in internal velocity distribution and fluid inertia: 76° was optimal for 32 mm and 90 mm pipes to enhance flow guidance, whereas 75° was recommended for 110 mm pipes to maintain streamline smoothness and avoid flow separation. Power output increased markedly with higher fertigation solution density; main pipes with larger flow areas were more sensitive to density changes, but excessive density induced flow disturbances, vortex intensification, and backflow in smaller pipes, indicating that density must be carefully controlled. Power output also rose substantially with greater terrain height differences. For the 90 mm main pipe, the output reached approximately 2700 W under an 8 m head difference, showing considerable power supply potential while maintaining a stable and orderly flow field. For the 32 mm branch pipe, the output was about 245 W, sufficient to power low-power sensor nodes, although local turbulence was observed at larger drops. The proposed transient–steady combined simulation method effectively identified the optimal impeller parameters, overcoming the limitations of single-indicator evaluation methods. Blade parameter adjustment proved to be an effective means of performance enhancement, while actual performance was strongly influenced by practical operating conditions. These findings provide practical guidance for the selection and operation of pipeline micro-hydro turbines in agricultural settings, particularly in hilly orchard irrigation systems.