Abstract: A recirculating system can be used to filter and clean the water by recycling it back to the fish culture tanks in modern aquaculture. A double-pipe water inlet mode has also been commonly used for the circular aquaculture tank in actual production in recent years. Taking the dual inlet mode as the research object, this study aims to explore the influence of the position and angle of the inlet pipe on the solid waste collection and hydrodynamic characteristics in the circular recirculating aquaculture tank. A model test was adopted using image processing and Particle Image Velocimetry (PIV) for a higher performance of the system. An investigation was made on the movement, accumulation, and flow field distribution of solid wastes in the recirculating aquaculture tank under different inlet pipe settings. A systematic experiment was then designed for three sets of inlet positions and nine groups of inlet angles under each group of position conditions. A camera was set directly above the tank, further to record the movement and collection process of the waste under different working conditions. The waste collection performance was then evaluated to quantify the amount of residual waste in the aquaculture tank. Meanwhile, the PIV technology was used to measure the flow field of the water layer 1 cm from the bottom of the tank under various working conditions. The hydrodynamic characteristics were associated with the average velocity (vavg), and velocity uniformity coefficient (U). The test results showed that: 1) The inlet setting outstandingly determined the waste collection and hydrodynamic characteristics of the tank, where they first increased and then weakened, with the increase of the position (d) of the inlet. 2) An optimal inlet angle depended mainly on the position of the inlet of the tank. Furthermore, the optimal angle of the inlet decreased gradually, as the position of the inlet increased. 3) An optimal performance of the system was achieved for the sewage collection and hydrodynamic characteristics of the breeding pond, where the setting distance of the inlet pipe was d=0, and the angle of the inlet pipe was 40°-50°. An optimal collection of solid wastes in the tank was also obtained, where the water inlet pipe was set at a distance d=1/4r and the angle was 20°-30°. Furthermore, an optimal sewage collection and hydrodynamic characteristics of the breeding pond was achieved, where the setting distance of the inlet pipe was d=1/2 r, and the angle of the inlet pipe was 10°-20°. Consequently, an optimal combination of parameters was that the inlet pipe position of d=1/4r, and the inlet pipe angle of 20°-30°, indicating the optimal sewage collection and hydrodynamic characteristics in the aquaculture pond. The finding can also provide a strong reference for the inlet setting of the recirculating aquaculture tank in the industrial circulating water.