In order to develop a numerical simulation of floor impact sound transmission via a floor structure that includes sound absorption materials, floor impact sound transmission via a composite floor structure composed of concrete slab, suspended ceiling plate, and an array of Helmholtz resonators inside a sandwiched air layer is modeled by the discrete wave-based numerical method of the vibroacoustic finite-difference time-domain (FDTD). As a preliminary study, the reverberant sound absorption coefficients of absorbers that contain arrayed resonators are simulated and compared to empirically measured values. The accuracy of the estimated sound absorption coefficient is found to depend largely on the diffuseness of the sound field in the simulated sound field as well as in reality. Thereafter, the floor impact sound generated by a floor structure that contains an array of resonators inside a sandwiched air layer between the floor slab and the ceiling plate is simulated, and relatively good agreement between the calculated and measured results for the improvement of the impact sound pressure levels caused by the installation of the resonators was confirmed. This suggests the applicability of the vibroacoustic FDTD method to sound-insulation prediction of the floor impact sound.