Abstract: The grille located in the lower part of the train body is usually easy to form a grille-cavity structure with the equipment bay’s surface. The problem of flow-acoustic coupling resonance of this structure is more prominent when the train runs at high speed. It is necessary to further analyze the flow-acoustic coupling mechanism of the structure. Therefore, the skirt plate with the grille, which is located in the lower part of the train body and can be simplified to a grilling-cavity structure, is taken as an example. And the Delayed Detached Eddy Simulation (DDES) is used to analyze the grille-cavity structure’s aerodynamic noise generation mechanism, flow field, and sound field. The results show that the shear oscillation at the opening of the grille-cavity structure is more intense when the train is running at 400 km/h, especially near the impact edge of the cavity. From the spatial and frequency domain distribution of the global sound pressure level and the wave number spectrum of the turbulent pressure, it is found that the flow field of the square grille-cavity is always in a transition state of self-excited oscillation and the amplitude of oscillation in the global sound pressure level and wave number domain at different positions is always lower than that of the V-shaped and semi-circular grille-cavity. Considering the effect of the air outlet on the semi-circular grille cavity currently used, it is observed that the evolution of vortex clusters inside the cavity slows down significantly, which directly causes the global sound pressure level near the grille to drop by about 15 dB. It can be considered that the effect of air outlet has a significant effect on the reduction of near-field noise of the skirt plate with the grille.