In order to study the influence of the relative inflow distance (parameter C/B, C is the horizontal distance from inlet to sidewall, B is the width of the rectangular tank) on the flow field characteristics of the double-drain square arc angle aquaculture tank system under the pattern of single-inlet pipe, this paper, based on CFD simulation technology, applied Fluent pre-processing software Gambit to construct a three-dimensional numerical calculation model and RNG k-ε turbulence model to simulate the flow field in a recirculating aquaculture tank system. The physical model test shows that the numerical model could accurately simulate the flow field in the square arc angle aquaculture tank system, and the effective energy utilization coefficient is proposed to evaluate the effective energy utilization rate of the aquaculture tank system. The results indicate that the average velocity (a=0.05，P<0.0001) in the aquaculture tank system and the effective energy utilization rate could be effectively improved by adjusting the relative inflow distance. The findings indicated that when the parameter C/B is between 0.02 and 0.04, it is conducive to obtaining the optimal hydrodynamic conditions in the double-drain square arc angle aquaculture tank system, which provides a theoretical basis for the layout of the industrial recirculating aquaculture inlet pipe.