The input of seismic wave with different frequency has a significant impact on loess slope instability. On the basis of field investigation and experiments, the particle flow software PFC2Dwas used to explore the effect of seismic frequency spectrum on slope instability through the process of calibrating soil microscopic parameters, model establishment, seismic wave input and other processes. The results show that: 1. The low-frequency component of the input wave is the main frequency band that causes the slope instability, the slope has amplifying effect on the low-frequency input wave, and the slope has a "filtering" effect on the high-frequency input wave; 2. The instability of the slope will cause an increase in frequency components above 10 Hz; 3. The special structure of the slope is one of the main reasons for the instability of the slope. This result has theoretical and practical significance for earthquake landslide prevention and monitoring and early warning.