In order to deeply explore the complex hydrodynamic characteristics of bigeye tuna （Thunnus obesus ） and provide a theoretical basis for the bionic design of low-drag fishing gear and the optimization of longline fishing operation parameters， this study takes bigeye tuna as the research subject. Based on its body shape characteristics， a three-dimensional numerical model was constructed using Solidworks software， and a silicone physical model of the fish was produced. By combining numerical simulation with flume model experiments， the study systematically analyzed the hydrodynamic properties， flow velocity distribution， and surface pressure distribution of bigeye tuna under different flow velocities and attack angles. The results indicate： （1） at a 0° angle of attack， the velocity field is symmetrically distributed， characterized by high velocities in the mid-body region and lower velocities at the head and tail. As the angle of attack increases， the high-velocity region shifts towards the leeward side of the fish body， while the high-velocity region on the windward side shifts rearward. When the angle of attack exceeds 25°， the high-velocity region on the leeward side expands， and the low-velocity region on the windward side encompasses the windward surface. Simultaneously， a distinct high-velocity region emerges between the dorsal fin and the caudal fin； （2） as the angle of attack increases， the region of positive pressure on the windward side of the bigeye tuna expands， and the region of negative pressure on the leeward side also increases. When the angle of attack exceeds 20°， positive pressure predominates over nearly the entire fish body； however， negative pressure intensifies in the dorsal and abdominal regions and at the trailing edge of the first dorsal fin. On the leeward side of the fish body， the head region exhibits positive pressure at angles of attack below 15°. However， as the angle of attack increases （from 0° to 45°）， the positive pressure area coverage decreases from 14.64% to 5.61%， while the negative pressure region expands. In contrast， the caudal peduncle consistently maintains positive pressure. This study indicates that the flow velocity and pressure distributions of the bigeye tuna are closely related to its body morphology and swimming posture， providing a significant theoretical basis for further exploration of efficient swimming mechanisms in fish. Moreover， this study conducts an in-depth analysis of the hydrodynamic role of fins， offering a reference for the optimization of bionic robot fish design and the improvement of fishing gear and methods.