Abstract: To solve the problems of high power consumption and low oxygenation efficiency of existing aquaculture aeration equipment, we designed a waterwheel-type solar aerator. Based on computational fluid dynamics, a numerical model of the aerator was established to verify and optimize the feasibility of the design. The validity of the numerical model was verified by physical model hydrodynamic test, with a focus on analyzing the influence of impeller speed on the flow field characteristics around the aerator. The results show that with the increase of the impeller speed of the aerator, the water flow velocity was obviously improved, and there was a large gradient difference, and the turbulence phenomenon became pronounced. The flow velocity on the monitoring surface 1–3 m near the impeller was concentrated around 1.0 m·s⁻¹, where the flow was unstable and circulation was obvious; while at 5 m from the impeller, the flow velocity was concentrated around 0.5 m·s⁻¹, with minimal fluctuation and stable flow. Due to the influence of the impeller, there was an obvious circulation phenomenon. With the increase of impeller speed, the average horizontal velocity at 1 m, 3 m and 5 m behind the impeller increased from 0.362 m∙s⁻¹, 0.402 m∙s⁻¹ and 0.447 m∙s⁻¹ to 0.521 m∙s⁻¹, 0.604 m∙s⁻¹ and 0.661 m∙s⁻¹, respectively, and the amplitude increased from 0.059 m∙s⁻¹, 0.044 m∙s⁻¹ and 0.033 m∙s⁻¹ to 0.082 m∙s⁻¹, 0.054 m∙s⁻¹ and 0.043 m∙s⁻¹, respectively. As the impeller speed of the aerator increased, the turbulence was significantly enhanced, particularly at the impact zone between the liquid and the free surface. This produced a large number of microbubbles, promoted liquid film renewal, prolonged the oxygen dissolution process, improved the oxygen mass transfer efficiency, and thus significantly strengthened the aeration performance. The research results provide a theoretical basis and technical support for the optimal design of energy-saving aerators.