The surrounding fictitious soil pile model was proposed to simulate the interaction between pile and pile soil plug, and the vertical dynamic model of the pile and cement soil plug was built, considering the strong cohesiveness between the pile and inner cement soil. The analytical solution in the frequency domain and the semi-analysis in the time domain of dynamic response of pile top under simple harmonic excitation were derived by impedance function transfer method. The reliability of the solution was verified by comparing with that of 3D finite element model. A parameter study was conducted to investigate the influence of cement soil parameters on the dynamic characteristics at pile top. Laboratory tests on cement soil and field tests were performed to investigate the influence of inner cement soil on low-strain test curves of pile, and the key parameters in the model were fitted and inverted based on the measured curves. Results show that the reflection signal from the pile tip becomes weaker and the integrated velocity of the pile becomes smaller with the increase of the height of cement soil plug. However, the reflection signal from the pile tip becomes weaker and the integrated velocity of the pile becomes bigger slightly with the increase of the modulus of the cement soil plug. The size of fictitious soil pile obtained by inversion keeps stable but the damping coefficient shows big difference with that from empirical formula. The measured curves show a good agreement with calculated curves, which indicates that the proposed theoretical model can well simulate the dynamic interaction between piles and inner cement soil.