The amplification effect of ground motion on infrastructure found in loess sites was investigated in this study. Taking a simply supported beam bridge as the research object, a pile-soil-bridge model considering the horizontal coupling effect of the El-Centro wave was established based on finite element theory. The analysis focused on acceleration response, spectral characteristics, and displacement response, clarifying the pile-soil interaction characteristics in loess areas. The results reveal that the relative pile-soil displacement and the peak acceleration of pile foundation show an apparent increasing trend with the increase in peak ground accelerations (PGA). Furthermore, as the elevation rises, the PGA amplification factor and Fourier amplitude increase gradually, while the predominant frequency of structure gradually shifts to the low-frequency direction. Compared with the far-field soil, the peak acceleration of loess soil around the pile in the range of 0-20 m increases by 30.87%. With the increase in pile length, the relative pile-soil displacement and the acceleration response of the pile foundation also show an obvious increase. Furthermore, the increase in pile diameter can effectively reduce the relative displacement of pile and soil and a structure's acceleration response.