Background/Introduction <p>Foam core composite sandwich structures are widely used in aerospace, automotive, and civil engineeringsectors, where natural frequency is a key measure of their dynamic performance.</p> Purpose <p>In this study, the influence mechanism of pore distribution and defect parameters on the natural frequency of suchstructures was investigated by experimental experiments and finite element analysis (FEA).</p> Methods <p>The vibration characteristics of the foam core composite sandwich panels were analyzed using a semi-analyticalapproach combining lamination theory and an improved Fourier series method, which was verified and complementedby finite element analysis (FEA) and experimental modal testing. Experimental tests mainly focused on modalmeasurements of foam-core composite panels with single round hole defects. Furthermore, the influence of other poredistribution and defect parameters was systematically studied by finite element analysis.</p> Results <p>The experimental results show that the finite element analysis model is verified, with a natural frequency deviationbetween 0.85% and 6.53%, including validation through foam core tensile tests and modal measurements. It was foundthat pore distribution affects the natural frequency by altering the elastic modulus and density, with a more significantimpact on low-order vibration modes. Additionally, core density and defect parameters (size, position, shape, quantity)also affect natural frequencies due to changes in structural stiffness and mass distribution, especially in low-ordermodes.</p> Conclusions <p>This study provides a theoretical basis for the dynamic design optimization and performance evaluation of foam corecomposite structures.</p>