Basement-addition for existing building plays a crucial role in alleviating urban land shortage. However, the disturbance induced by basement-addition construction to the stability of the building foundation and superstructure has not been well understood. The objective of this paper is to investigate the performance of typical structural components involved in a basement-addition project. They include the columns in the superstructure, the strip foundation beneath the columns, and the piles used for reinforcing the strip foundation during excavation. A three-dimensional finite element model is established, using a basement-addition project of an existing building as a case example. The calculated results by the finite element model align well with the measured data, confirming the model's validity. Based on this, the stress and deformation characteristics associated with the selected structural components during basement-addition construction are investigated. The findings indicate that the stress and deformation characteristics of the structural components are highly sensitive to the depth of the foundation pit excavation, with these characteristics intensifying as excavation depth increases. The excavation of the initial soil layer has the most significant impact. Upon completion of the excavation, the maximum settlement values for the strip foundation (SF), column foot, and pile are -18.6 mm, -13.79 mm, and -16.1 mm, respectively. The underground diaphragm wall (UDW) exhibits maximum vertical and horizontal displacements of 7.6 mm and 18.1 mm, respectively. The pile primarily experiences compressive internal forces, with its axial force showing little sensitivity to excavation depth. The pile's maximum bending moment, shear force, and axial force are 21.2 kNm, 34 kN, and -2,481 kN, respectively. The internal forces and deformations of structural components demonstrate distinct spatial distribution patterns, with values increasing closer to the foundation pit's center. Therefore, it is crucial to enhance monitoring of the displacement and internal forces of the central components of the foundation pit to prevent engineering accidents. These research findings will contribute positively to the design optimization and construction guidance of similar engineering structures.