To address dust escape during the unloading process of grab ship unloaders, this study endeavors to develop an efficient unpowered dust suppression structure. Firstly, the formula for dust suspension velocity is derived to clarify the conditions governing dust diffusion. Subsequently, four two-dimensional models of the dust suppression structure are designed, and comparative simulation analyses are performed to optimize the structure—with a focus on parameters such as guide plate width and inlet width. Finally, a three-dimensional model is constructed based on the optimal two-dimensional configuration (Structure IV), and its rationality is validated using the FLUENT-DPM model to observe particle movement trajectories. The results demonstrate that the unpowered dust suppression method is feasible, with Structure IV—characterized by filleted corners and widened channels—exhibiting the optimal dust suppression performance, reducing the outlet airflow velocity to approximately 0.95 m/s. Two-dimensional simulations enable preliminary evaluation of structural accuracy, while three-dimensional simulations realistically replicate actual operating conditions. The FLUENT-DPM model clearly reveals that large particles tend to settle after rebounding, whereas small dust particles may escape with the airflow.