Abstract: This study investigates the noise reduction mechanism of an aero-engine nacelle inlet acoustic liner and constructs a Kriging surrogate model for its optimization design. First, a two-dimensional axisymmetric numerical model for acoustic propagation is established, employing the linearized Euler equations to describe sound wave propagation in a non-uniform background flow field (inlet Mach number 0.2, fan-stage Mach number 0.5). Second, combined with duct acoustic mode theory, the cut-off characteristics and propagation behavior of acoustic modes at different frequencies are analyzed. The acoustic field distribution is solved using impedance boundary conditions for the liner, and the noise reduction mechanism is interpreted by comparing mode contour plots for different circumferential modes and frequencies. Results indicate that the acoustic liner disrupts the symmetry of the incident mode while exciting higher-order radial modes, thereby dissipating acoustic energy. Finally, using transmission loss as the evaluation metric, a Kriging surrogate model coupled with a genetic algorithm is used to optimize four structural parameters: cavity depth, faceplate thickness, orifice diameter, and porosity. The established surrogate model demonstrates high predictive accuracy (R² = 0.94). Results show that the optimized liner configuration (cavity depth 18 mm, faceplate thickness 1.01 mm, orifice diameter 1.2 mm, porosity 3.2%) achieves improved overall transmission loss over the 0–4000 Hz frequency range. Modal pressure contour plots and transmission loss curves further confirm that the optimized design more effectively improves the overall energy distribution of the acoustic field.