The integrity of the netting in aquaculture cages is crucial for maintaining farming efficiency and ecological balance. Damaged netting not only reduces performance but may also lead to the escape of cultured organisms, resulting in both economic and ecological losses. To assess the impact of netting damage on hydrodynamic characteristics and flow fields, and to explore preliminary methods for damage localization and severity assessment to guide the optimization of cage maintenance strategies, a unidirectional fluid-structure interaction numerical model based on ANSYS Workbench has been established. The model simulates the flow field around the netting in the fluid domain, obtaining data such as pressure on the netting surface, which is then transferred to the solid domain to calculate the deformation and stress distribution of the netting under fluid loads, achieving hydrodynamic responses of netting with varying degrees of damage at flow velocities of 0.1 to 1 m/s. The results show that the drag of the netting increases with the square of the flow velocity, and the increase in damage degree leads to a decrease in drag, especially when the damage is significant. The flow velocity decay rate is relatively stable under different damage degrees, indicating that the impact of netting damage on the overall flow velocity decay rate is limited. Under a flow velocity of 0.5 m/s, the influence of damaged netting on the flow velocity decay zone in front of the netting is limited, but damage makes the phenomenon of accelerated flow between the net lines more apparent, causing significant interference with the flow velocity decay zone behind. The overall maximum deformation and maximum stress of the netting do not change significantly with the increase in damage degree, but the stress near the damaged area increases significantly. This study not only enhances the understanding of the hydrodynamic characteristics of the netting but also provides important technical support for the design, performance evaluation, and risk management of aquaculture cages.