To explore the gas - liquid - solid three - phase flow characteristics during the operation of the pneumatic lift sludge suction equipment in the hatchery tank and establish a structural optimization method for the pipeline gas lift sludge suction device, the Fluent computational fluid dynamics tool was used. Based on the Euler multi - phase flow model and the dense discrete phase (DDPM) model, the influence of the structural form of the pneumatic lift pool bottom sludge suction equipment on the sludge suction performance was analyzed. The test results show that: the gas - liquid - solid three - phase flow process within the air - lift pipeline can be divided into the initial stage, pressure relief stage, lifting stage, and stable stage. The diameter, number, and spacing of the openings in the air - lift pipeline, as well as the height from the bottom, directly affect its sludge suction performance. Appropriate adjustment of the opening spacing can enhance the effectiveness of sludge suction. The optimal diameter for the openings in the air - lift pipeline is approximately 4 mm. Increasing the number of openings in the air - lift pipeline by 2.5 times results in a 27.2% decrease in the efficiency of the air - lift system. In contrast, increasing the height of the pipeline from the bottom by 3 times leads to a 31.6% reduction in system efficiency. Therefore, it is advisable to avoid increasing the number of openings and the height from the bottom in the air - lift pipeline.