To investigate the influence of soil-structure interface parameters on the seismic dynamic response of underground utility tunnels, in this study we built a dynamic finite element numerical model to probe the influence of changes in seismic input motion and interface reduction factors on the internal force and acceleration in utility tunnels. In the model, an optimized combination of boundary conditions was adopted wherein the excitation-applied side was a fixed boundary, the excitation-free side a viscous boundary, and the rest free-field boundaries. A small-strain stiffness model was employed as the constitutive soil model, a modified Goodman element was used to model the interface, and the dynamic load took into account three conditions:the effects of Rayleigh waves, the effects of bottom seismic waves (as those in Upland, California), and the combined effects of the two. The results showed that when the reduction factor remained unchanged, the structural internal force was greater under dynamic than under static force. Therefore, the situation wherein there is an increase in internal force under seismic loads should be considered in the design of utility tunnels. When the reduction factor increased, the extreme value of the sagging moment decreased, the extreme value of hogging moment increased, and the peak acceleration value increased. When the reduction factor remained the same, the extreme value of the structural internal force generated by bottom seismic waves was higher than that generated by Rayleigh waves. However, under the combined effect of Rayleigh and seismic waves, the extreme value of the structural internal force generated differed very slightly from that when only seismic waves were input. The research findings are expected to provide a reference for elaborate numerical simulations of the seismic response of underground utility tunnels and their seismic design.