With the rapid development of the city, the land becomes more and more scarce. Especially for the mountain cities, it has to consider building the buildings on the rock slope, so it is of great practical significance to study the interaction between the rock slope foundation and the upper building. The finite element method is used to study the co-influence of the layer number of upper structure, rock strength and building distance on the internal force of pile raft foundation under the interaction, and comparisons are made with the conventional design method without considering the interaction. The calculation results show that the main stress of raft is considered to be less than conventional design, and the maximum principal stress is transferred from the center to the edge of raft. With an increasing number of superstructure floors, the contribution of the superstructure to the stiffness of the raft is increased, the adjustment of the stress of the raft is enhanced, the reverse force of the substrate diffuses around, and the stress distribution of the raft is even more uniform.