Abstract: With the progressive saturation of nearshore aquaculture resources, the aquaculture industry is gradually shifting toward deeper and more remote offshore waters. To accommodate the complex and variable marine conditions in deep-sea environments, higher structural safety requirements are being imposed on aquaculture facilities. Among these, the safety performance of the PET net panel directly affects the operational reliability of aquaculture cages. This study investigates the deformation behavior and stress distribution characteristics of polyethylene terephthalate (PET) net panels—commonly used in deep-sea aquaculture systems—under various hydrodynamic conditions. Based on ANSYS simulations, the effects of net panel structural parameters (twine diameter and mesh size), flow velocity (v = 0.3, 0.6, 0.9, and 1.2 m/s), and angle of attack (α = 22.5°, 45°, 67.5°, and 90°) on the deformation and stress distribution of PET net panels within a square frame were systematically analyzed. The results indicate that under identical solidity, twine diameter has a more significant impact on the deformation and equivalent stress of the PET net panel compared to mesh size. At a flow velocity of 1.2 m/s and an angle of attack of 90°, the deformation and equivalent stress resulting from each 1 mm increase in twine diameter were 1.60 times greater than those caused by a 20 mm increase in mesh size. Across different flow conditions, both the deformation and equivalent stress of the PET net panel showed positive correlations with flow velocity and angle of attack. When the angle of attack was 90°, the growth rates of deformation and equivalent stress within the flow velocity intervals of 0.3-0.6, 0.6-0.9 and 0.9-1.2 m/s followed a ratio of 1.00∶1.65∶2.31, which was independent of the net panel structural parameters. At a flow velocity of 1.2 m/s, the growth rates of deformation and equivalent stress between 22.5° and 67.5° were significantly higher than those between 67.5° and 90°. Moreover, the combined influences of net panel structural parameters, flow velocity, and angle of attack on the deformation and stress distribution characteristics shared a consistent pattern: the maximum deformation was concentrated in the geometric center of the PET net panel. The equivalent stress near the net frame exhibited a gradient increase from the four corners toward the symmetry axis, while along the symmetry axis, stress decreased from the frame toward the center of the net panel. For individual twines, stress increased from the middle toward both ends, reaching a peak at the twisted double-strand nodes. This study elucidates the effects of flow velocity, angle of attack, and mesh structure (mesh size and twine diameter) on the deformation characteristics and stress distribution of PET net panels, providing valuable data support for further evaluation of the structural safety of deep-sea aquaculture equipment.