A numerical model of the liquefaction horizontal free-field shaking table test was developed based on the completed large-scale shaking table test of liquefaction horizontal free field using the OpenSees finite element platform, and the numerical model was verified. Based on this, a free-field numerical model of the overall inclined foundation was established, and the non-cyclic dynamic response of the liquefaction lateral spreading site and the mechanism of liquefaction-induced lateral spreading were discussed. The results show that the established numerical model can effectively simulate the seismic response in liquefiable sites. There was significant relative displacement at the interface between liquefiable loose sand and overlying non-liquefiable layer. In the inclined site, the strain accumulation of saturated sand soil starts from the upper part of the loose sand layer and gradually develops downward. The increase of excess pore water pressure was not completely coupled with the accumulation of non-cyclic strain of the soil. The non-cyclic lateral displacement was controlled by the middle parts of the site. In the process of soil liquefaction, when the shear stress along the sliding surface is less than the initial static shear stress, lateral spreading starts, and the shear stress ratio of the saturated loose sand layer is in the range of 0.04−0.06, which is slightly smaller than the initial static shear stress ratio. In addition, it is found that liquefaction-induced lateral spreading requires a certain site inclination (greater than 0.5º). The lateral displacement of soil conforms to the cosine distribution pattern. With the increase of site inclination, the contribution of liquefiable deep soil to the overall lateral displacement is more significant.