Abstract: Evaluating the impact of site damage on building damage is a difficult subject, and the impact of site damage has not been considered in most of the current earthquake damage mitigation techniques, such as structural seismic damage prediction and disaster reconstruction. Lateral permanent displacement (deformation) of soil is a common type of site damage, which causes serious earthquake damage to buildings. A simplified model of a 6-story and 2-span reinforced concrete frame structure was constructed by OpenSees software, and the impact of lateral permanent foundation displacement on seismic damage during an earthquake was assessed by inputting displacement time courses of different strengths and permanent displacements. The calculation results show that: (1) the impact of lateral permanent displacement of the foundation on the maximum story-drift angles of the bottom story is significant, even if only a lateral permanent displacement of 0.05 m occurs on the foundation with the seismic intensity is less than 0.4g, the maximum story-drift of the bottom story is much larger than that of the condition which no permanent displacement occurs on the foundation; When the seismic intensity is increased to 0.4g, the maximum story-drift of the structure occurs at the second story, at this time the impact of permanent displacement is smaller than that of seismic intensity; (2) When the permanent displacement of 0.1 m occurs in the foundation, the permanent displacement has a decisive influence on the damage level of the structure, and the influence is mainly reflected on story-drift of the ground floor, little impact is showed on the damage level of other floors; (3) Through numerical calculation of the simplified model, the impact of lateral permanent displacement of the foundation on the damage level of the structure is analysed to explain the phenomenon that site damage in earthquakes mostly aggravates the seismic damage of the structure.