Abstract: In order to improve the flow field characteristics in dual-drain square aquaculture tank, we combined arc angle and straight edge to optimize the flow field, so as to provide better aquaculture equipment for the recirculating aquaculture industry. We applied computational fluid dynamics technology to simulate the flow field in dual-drain aquaculture tanks, and evaluated the effect of relative arc to width ratio (R/B, R is the radius of arc angle, B is the side length of tank wall) on the flow field characteristics in the tanks by analyzing corrected velocity v₀ and uniformity coefficient UC₅₀. The results show a same rule under different conditions of underflow split ratio (The percentage of outflow from the center outlet at the bottom of the tank in the total outflow). The average velocity in the square arc angle aquaculture tanks with 0.2≤R/B<0.4 was about twice than that in the square aquaculture tanks for the same water exchange rate, but there was no significant difference compared with the circular aquaculture tanks. According to the analysis of flow field uniformity, the square arc angle aquaculture tanks with 0.2≤R/B<0.4 had higher uniformity coefficient, and even higher than that of circular aquaculture tanks. The research indicates that the area of lower velocity caused by the right angle in the square aquaculture tanks reduced effectively by the arc angle in the square arc angle aquaculture tanks, and higher space utilization rate was retained. The advantages of the square aquaculture tank and the circular aquaculture tank are fully combined in the square arc angle aquaculture tank, which solves the problem of poor flow pattern in dual-drain square aquaculture tank, with good industrial popularization and application value.