Abstract: This study conducts vertical steady-state harmonic excitation model tests of suction bucket foundations in dry and saturated sand under different excitation force amplitudes and aspect ratios. The amplitude-frequency characteristics of bucket-top displacement are analyzed to elucidate the vertical vibration behavior of a single bucket foundation embedded in sand. The results indicate that the overall shapes of the frequency-response curves of the bucket-soil system remain consistent across test conditions, with significant amplification occurring near resonance. With increasing excitation amplitude, the bucket-top response increases, whereas the resonance frequency remains essentially unchanged. An increase in the length-to-diameter ratio markedly reduces the bucket-top displacement response, and its influence on resonance characteristics is mainly manifested in low-order modes. Compared with the dry-sand condition, the saturated-sand condition exhibits lower resonance peaks and flatter peak shapes. The findings provide a basis for evaluating the vertical dynamic performance of bucket foundations in saturated seabed soils.