In the loess area, the bearing capacity of rigid pile composite foundation is mainly determined based on the load test of single pile composite foundation. However, it has been observed that there is a significant difference in settlement between on-site loading tests in settlement between on-site loading tests and the actual settlement of the building. In order to identify the reasons for the difference in settlement between single-pile composite foundation and pile group composite foundation, and to lay a foundation for revising the results of loading tests for single-pile composite foundation, this article studies the bearing differences between single pile composite foundation and group pile composite foundation under high-rise building loads. Based on an example of a first-class high-rise building, it was found that although the settlement results of the loading test were smaller, the high-rise building experienced excessive settlement. Therefore, it is necessary to further establish a finite element model considering the pile-soil interaction for single pile composite foundation and pile group composite foundation, and compare and analyze the differences in pile axial force and side friction. The difference in bearing capacity is due to the higher load borne by the soil between piles in the pile group composite foundation. The soil around piles generates downward movement relative to the surface of the pile. This will lead to a decrease in the lateral friction resistance of the pile, thereby weakening its bearing capacity and increasing its vertical settlement. Resulting in the difference in settlement between the loading test and the actual post-construction settlement.