Abstract: Aiming at the problem of pile-soil separation and large lateral deformation of pile induced by deformation failure of foundation soil under the earthquake action, a new environmentally friendly green reinforcement material lignin was used to reinforce the foundation soil of loess engineering site. Based on laboratory test and numerical simulation, considering the pile-soil interaction and the reinforcement depth of the modified loess, the seismic performance of pile in loess engineering site modified by lignin was studied. The results show that: (1) The depth h of lignin-modified loess has little effect on the first-order natural frequency of the pile-soil interaction system, but has a great influence on the second-order frequency. After h>2m, the second-order frequency of the system increases significantly. (2) The maximum axial force at the bottom of the pile is the smallest, while the maximum axial force at the middle of the pile is the largest, and the maximum value increases with the increase of h. The maximum value of the maximum bending moment appears at the 1/4 pile length from the bottom of the pile, from the two aspects of the maximum bending moment and the inflection point of the pile, and decreases with the increase of h. (3) The increase of h has a positive effect on the reduction of pile displacement. With the increase of h, the displacement of pile decreases as a whole, and the displacement of pile head at h=12 m is only 27% of that at h=0 m. (4) The side friction resistance of the pile will have a sudden change at the interface of the soil layer. The reinforced loess layer provides a great contribution to the pile-soil interaction and increases the support of the pile periphery soil on the pile. When h=4 m, the pile periphery soil has the strongest overall support on the pile. (5) The seismic performance of the pile foundation can be improved from II to I when the h exceeds 1 m. It can be considered that the optimal reinforcement depth is 4 m for the model in this paper, considering the damage and displacement of pile after earthquake and the economy of foundation soil reinforcement. The relevant conclusions can provide reference for the seismic performance of similar bridge pile foundation reinforcement.