Abstract: As an important tool for cleaning fouling organisms on aquaculture net cages, net cage cleaning robots operate within complex hydrodynamic environments. To achieve stable and low-power attachment to the net during underwater operation, this paper proposes a chain-claw net cage cleaning robot based on a comparative analysis of existing designs. Given the robot's pronounced non-streamlined and multi-bar geometric features, a targeted hydrodynamic analysis is essential. A numerical investigation was conducted using Computational Fluid Dynamics (CFD), in which a simplified robot model and a computational domain with boundary-layer meshes were established. The realizable k-\varepsilon turbulence model, well-suited for separated flow simulations, was employed to define the numerical simulation parameters. A simplified robot model was developed and a computational domain with boundary-layer meshes was established, and numerical simulation parameters were defined using the Realizable k-\varepsilon turbulence model, which is suitable for separated flow simulations. The flow field around the robot was simulated under different forward velocities ranging from 0.1 m·s⁻¹ to 1.0 m·s⁻¹ and various horizontal inflow angles from 0° to 180°, and the hydrodynamic drag force and drag coefficient were analyzed and calculated. The results show that during linear motion, the drag force increased with increasing velocity, while the drag coefficient tended to stabilize at approximately 0.85 when the velocity exceeded 0.4 m·s⁻¹. Under different horizontal inflow angles, the drag force was positively correlated with the projected frontal area, reaching a minimum of 3.46 N at 0° and a maximum of 6.09 N at 120°. The findings provide theoretical support for the power system design, motion control, and structural optimization of net cage cleaning robots.