Abstract: To improve the suitability for fish, we conducted a study on the hydrodynamic characteristics of the internal flow field by different water inflow methods. Firstly, we constructed a numerical model of the fish tanks in a 300 000-ton aquaculture vessel by using Computational Fluid Dynamics (CFD) technology, and validated its feasibility of the numerical method. On this basis, we analyzed the hydrodynamic characteristics such as flow velocity distribution, fluid uniformity and resistance coefficient, and evaluated the effects of the area proportion of flow velocity suitable for fishing and the state of bottom flow field on the fitness level of Pseudosciaena crocea. The results indicate that changes in the number of daily water exchanges affected the flow velocity magnitude within the aquaculture tank significantly. As the number of daily exchanges decreased from 16 to 10, the average flow velocity inside the tank dropped by 46.7%. Conversely, the changes in the number of inlet ports had a considerable impact on the uniformity of water flow. When the number of inlets reduced from 16 to 4, the fluid uniformity index inside the tank decreased by 18.4%. When altering the placement of inlet ports, it is crucial to pay attention to the interactions between the inflow jets. Comprehensive analysis shows that it is the most beneficial for the culture of P. crocea with 16 times of daily water change, and by evenly arranging the 16 water intakes at the cut corners of rectangular tank.