In this paper, the effects of adjacent building on soil-structure interaction of spread foundation are studied by the thin layered element method combined with flexible volume substructure method. The effects of the adjacent building on the impedances and foundation input motions are examined. The inertia effect of adjacent building prominently appears on horizontal impedance and rotational foundation input motion. The effects of the factors such as the distance between the foundations, the size and height of the adjacent building, the embedment depth, the stiffness of the backfill soil and three buildings interaction are also analyzed in this paper.