Abstract: Abstract: Traditional pressure sand filter after long time working intercepts large amounts of solid particles and leads to difficult backwash. In order to solve these problems, this study developed an airlift sand filter that can backwash itself while operating by optimizing a traditional filter. The airlift sand filter itself had filtration, separation, flotation, and self-cleaning functions, and could replace the traditional sand filters such as filter cell without valve, mechanical air flotation and other physical filtration device in aquaculture workshop. In the airlift sand filter, quartz sand (in diameter of 1-2 mm) was used as the filter medium, and the aquaculture sewage was flowed upward slowly from the bottom, thus quartz sand could intercept the suspended solids. Meanwhile, the fixed flow gas flowed from the bottom pushed dirt and quartz sand upwards simultaneously. During this process, sand and water were sufficiently contacted with each other. The interaction force between the sand and seawater resulted in production of a large number of bubbles. The suspended solids were then wrapped with the bubbles while quartz sand was cleaned by the sand washing device on the top of the system. The cleaned sand fallen back to the filter system by the gravity, and the suspended solids and waste water flowed out of the outfall. The airlift sand filter has the advantages of simple equipment, convenient operation, backwash without stopping the equipment, smooth and continuous system running, low energy consumption and easy to maintain and repair. The efficiency of the airlift sand filter used for marine recirculating aquaculture systems of the suspended solids (SS) and chemical oxygen demand (COD) was tested. Results showed that removal efficiency of SS and COD by this filter was 41.31% and 34.04%, respectively. Before the filtration, the number of large particles suspended solids (60 μm or higher) was 11.1%, its mass fraction was 71.77% and its mass concentration was 93.53 mg/L. The water processing decreased the number, mass fraction, and mass concentration of the large particles suspended solids to 0.68%, 38.07%, and 15.72 mg/L, respectively. At the beginning of the test, the number of micro particles (60 μm or less) was 88.92%, its mass fraction was 28.23%, and its mass concentration was 36.79 mg/L. After the treatment, the micro particles below 30 μm accounted for 87.45%, its number of mass fraction was 13.61%, and its mass concentration was 5.62 mg/L. These results suggested that the effect of particulate removal treatment was obvious. Meanwhile, the treatment also reduced the content of ammonia nitrogen and nitrite in the system. After filtration, the suspended solids in recirculating aquaculture systems were ≤67.33 mg/L, meeting the requirements of the water treatment in marine recirculating aquaculture workshop by China.