Seismic spectrum, as one of the three elements of ground motion, has a significant influence on the instability of loess slopes. On the basis of field investigation and collection of research area data, a generalized numerical model of typical slope site is established, and a reasonable dynamic artificial boundary is selected to explore the influence of ground motion spectrum on the stability of loess slope. The following conclusions are obtained : (1) The slope acceleration is greatly affected by the input frequency of ground motion. Under different frequency ground motion input, the acceleration peak amplification coefficient curves of different monitoring points show different trends. At the same time, the velocity and displacement are greatly affected by the input frequency of ground motion, but the velocity and displacement curves of each monitoring point at different frequencies have the same trend; (2) Low frequency vibration is the key frequency band to induce slope instability, and the slope is not easy to fail under high frequency vibration. The slope has an amplification effect on low-frequency seismic waves and a certain ' filtering ' effect on high-frequency seismic waves; (3) With the increase of elevation, the displacement of slope motion increases, and the lower the input frequency of ground motion, the more obvious the increase effect. This study provides a reference for the enhancement of loess slope stability, and has theoretical and practical guiding significance for earthquake landslide disaster prevention and mitigation.