In the process of industrial circular recirculating aquaculture, solid wastes will greatly harm the farmed fish. Improving the self-cleaning ability of the recirculating aquaculture tank is an effective way to remove the solid wastes in the recirculating aquaculture tank. The self-cleaning ability of recirculating aquaculture tank refers to the process of automatically collecting solid wastes to the center of the tank by adjusting the water flow in the tank. A series of indoor experiments have been conducted to study the effect of water inlet angle on the self-cleaning ability of the recirculating aquaculture tank, and the particle imaging velocimetry (PIV) is used to measure the flow field. In the test, a total of 9 cases of different setting angles of the inlet pipe were designed for the circular tank with a symmetrical dual water inlet mode. A camera set directly above the tank is used to record the collection process of the solid wastes under different cases. By analyzing the movement process of the solid wastes and the amount of residual solid wastes in the tank, the effect of the setting angle of the inlet pipe on the solid waste collection process and self-cleaning ability in recirculating aquaculture tank have been quantified. The PIV system was used to measure the flow field in the water layer of 1, 2, 10, 19 cm from the bottom of the tank. By analyzing the flow pattern, resistance coefficient, velocity uniformity coefficient and other hydrodynamic parameters of the recirculating aquaculture tank, the mechanism of the setting angle of the inlet pipe on the solid waste collection process and self-cleaning ability in the recirculating aquaculture tank is clarified. The results show that: the setting angle of the inlet pipe obviously affects the self-cleaning ability of the recirculating aquaculture tank, and the self-cleaning ability firstly increases and then decreases with the increase of the setting angle. The self-cleaning ability of the recirculating aquaculture tank shows good performance under the cases of 45° and 50°; the setting angle of the water inlet pipe affects the self-cleaning ability of the recirculating aquaculture tank by affecting the velocity magnitude and flow pattern in the bottom water layer. The velocity magnitude rate determines whether the solid waste can be picked up, and the flow pattern determines whether the solid waste can be collected to the water outlet. Therefore, in aquaculture practice, it is recommended to set the angle of the inlet pipe of the tank similar to the research in this article to 45° to 50° working condition to improve the self-cleaning ability of the recirculating aquaculture tank and improve the comprehensive performance of circulating aquaculture.