To scientifically evaluate the seismic performance of soil nailed slopes in seasonal frozen areas, based on the theory equation of thermal-dynamics, a numerical model of soil nailed slope with viscoelastic artificial boundary in seasonal frozen area was established under earthquake load by using large-scale nonlinear finite element software ABAQUS. The acceleration response, displacement response, and axial force response of soil nails in summer and winter were compared and analyzed. The results showed that whether in summer or winter, the peak acceleration increases with the increase of the slope elevation and the peak value of excitation acceleration, and reaches the maximum at the top of slope in summer. In addition, under the action of seismic waves with different peak acceleration, the peak displacement responses at the same position are obviously different. When seismic wave with the same intensity is excited, the largest displacement shows at the top of slope in summer, indicating that the seismic load has the most obvious damage effect on the top of slope in summer. The axial force of soil nails has elevation amplification effect and slope amplification effect. The peak value of axial force at the end of soil nails gradually increases from the bottom of slope to the top. The numerical simulation model and conclusions in this paper can provide some reference for the seismic design of seasonally frozen soil slope supported by soil nails under seismic load.