<p>The dynamic response of underground cavities in layered sites to plane SH waves is a fundamental research topic in underground seismic engineering. Using the wave function expansion method combined with the plane wave spectrum superposition technique, this paper establishes an analytical model for a cylindrical cavity embedded in the substratum. The problem is reduced to a system of infinite linear equations and solved numerically using series truncation and complex damping. Accuracy verification and comparison with classical solutions confirm the reliability of the method. Parametric analysis demonstrates that the shear modulus ratio exerts a remarkable influence on the displacement distribution around the cavity, particularly within its low-value range. Overburden thickness and incidence angle jointly determine the displacement evolution law, and soft and hard overburdens exhibiting mirror-image patterns. Variations in cavity depth trigger periodic evolution of displacement responses. Additionally, the dimensionless frequency has a strong controlling effect on the dynamic behavior of the cavity, and the overburden layer produces an obvious amplification effect on the cavity response under high-frequency excitation. The findings provide a theoretical basis for the seismic design of underground structures in layered sites.</p>