Abstract: To address the demand for in situ tests of the low-frequency dynamic stiffness and frequency-dependent behaviors of a shallow foundation, this study introduced a method that integrates controlled-source continuous frequency-sweep with vertical velocity admittance. Specifically, vertical frequency-sweep tests were carried out within the frequency range of 10~110 Hz on a manually compacted foundation and an undisturbed soil foundation. The excitation force was back-calculated based on the accelerations of the hammer and vibrator baseplate, and the dynamic stiffness was estimated based on the vertical velocity admittance of frequencies below 20 Hz. Frequency-sweep tests were repeated three times for each foundation under initial frequencies of 10 Hz, 20 Hz, 40 Hz, and 60 Hz. The admittance curves agreed well over the swept frequency range, and variations in dynamic stiffness within the 10‒20 Hz frequency band were captured for both foundations. The results indicate that the dynamic stiffness decreased with increasing frequency for both foundations, with a greater amplitude observed in the manually compacted foundation. The proposed method can provide the equivalent dynamic stiffness of foundations under low-frequency vibration, thereby enabling the comparative assessment of the dynamics of foundations treated in different ways. Meanwhile, this method also offers a technical pathway for assessing the dynamic parameters of foundations under small strains.