Abstract: Large eddy simulation (LES) was used to investigate the effect of an external lateral disturbance flow on an air curtain. For an air curtain with an inlet velocity of Uj=3 m/s, the flow field characteristics were studied under three cases of lateral disturbance velocity Ud=0 m/s, 0.5 m/s, and 1.0 m/s, revealing the influence of the disturbance on the stability of the air curtain. The Q criterion and λ2 criterion were employed to identify vortex structures, and the shear-layer mode of air curtain oscillation was analyzed. Spectral analysis of pressure fluctuations at monitoring points in the air curtain showed that higher-order modes dominated the cavity flow in this study; the power spectral density (PSD) of the dominant mode decreased along the air curtain flow direction in an exponential manner, and the decay rate increased with increasing disturbance velocity. Dynamic mode decomposition (DMD) analysis of the pressure field in the mid-plane of the air curtain indicated that the number of unstable modes gradually increased with increasing disturbance velocity Ud, leading to a gradual reduction in the stability of the air curtain flow.