One of the main design constraints is to prevent damages to adjacent buildings, especially during excavation for basement construction. As excavation proceeds, the surrounding soils will move toward the excavation and their movement will induce bending moments and deflections in the existing pile groups. The existing pile response due to the excavation-induced lateral soil movements had been studied previously by using numerical analysis and laboratory analysis, but there are some parameters did not study. For this reason, this research studies numerically the interaction between existing pile groups and piles supporting excavation. Commercial program Plaxis 2D is used in the numerical analysis. This research contains two groups with different cases: piles supporting excavation only and quadruple-row of capped head existing piles are nearby a supported excavation. A parametric study was performed to study the effect of pile supporting excavation diameter, length, and excavation depth. Results indicated that as a result of increasing diameter of the pile supporting excavation, bending moment in the pile supporting excavation increases, however bending moments in the existing building piles decrease. Moreover, by increasing the excavation depth, the maximum bending moment increases in both pile supporting excavation and existing building piles but this bending moment does not occur at the same depth. Furthermore, the peripheral piles in the pile group always have higher bending moments than those of interior piles.