Abstract: A homogeneous and stable flow field is required to promote the healthy growth of the fish in the recirculating aquaculture systems. Among them, the structure of the inlet pipes can dominate the water inflow patterns and the distribution of the flow field in the aquaculture ponds. At the same time, there is also a great influence on the growth of the fish and the removal of suspended particulate matter, such as the uneaten feed and the feces. This study aims to investigate the impacts of the different structures of the inlet pipes on the flow field distribution in circular aquaculture ponds. The optimal structural parameters of the inlet pipes were determined for the uniform distribution of the flow field. A numerical model was established for the circular aquaculture pond using computational fluid dynamics (CFD) software. A series of simulations were then conducted to verify the structural parameters, including the number of the inlet pipes, the ejection angle of each inlet pipe, and the number of the jet holes on the inlet pipes. The uniformity of the flow field was evaluated, according to the uniformity coefficient of velocity distribution U50 as an assessment indicator. Orthogonal experiments were designed to obtain the optimal combination for the structural parameters of the inlet pipes in the circular aquaculture pond. Simultaneously, a recirculating aquaculture system was constructed in accordance with the optimal structure parameters of the inlet pipes. An aquaculture experiment was carried out on Micropterus salmoides, in order to verify the optimization. The flow field was then evaluated to monitor the water quality and the growth indicators of Micropterus salmoides samples in the aquaculture system. The experimental results demonstrate that the most uniform distribution of the flow field was achieved, when the circular aquaculture pond was equipped with three inlet pipes arranged at 120°, with six jet holes on each single inlet pipe and a jet angle of 45° for the inlet pipe. Three groups of Micropterus salmoides aquaculture experiments were conducted with different densities at the water flow velocity of 0.1 m/s. The concentration values of the nitrite and ammonia nitrogen were less than or equal to 0.2 and 0.3mg/L, respectively in the aquaculture pond. The turbidity values of the water were all lower than 0.3 NTU (nephelometric turbidity unit), indicating the high water quality and the low level of the suspended particles. The lowest feed coefficient of Micropterus salmoides samples with the three different density groups was 1.06, while the highest weight gain rate was 161.03%, and the highest survival rate was 100%. The flow field contributed to the weight gain rate of fish for the favorable survival rate of the fish population. The feed coefficient of fish was also reduced to facilitate the healthy growth of fish. The optimal structure of the inlet pipes was conducive to the uniform and stable flow field in a circular aquaculture pond. The suspended particulate matter was effectively discharged to maintain the water quality of the aquaculture water body. The finding can provide theoretical guidance to optimize the structures of the inlet pipes for the uniform flow field in a recirculating aquaculture system.