In order to investigate the adverse effects of eccentric loads on internally braced excavation pits and mitigate construction risks, a detailed analysis of deformation characteristics and underlying mechanisms is crucial for improving both the safety and cost-effectiveness of excavation projects. To quantify the influence of eccentric loading, an eccentricity coefficient was proposed. Numerical simulations were employed to systematically investigate the deformation patterns and mechanisms of excavation under various eccentricity coefficients. Furthermore, a gradient reinforcement method for the pit bottom soil was developed, specifically tailored to the deformation characteristics observed in eccentric conditions. The results show that the eccentricity coefficient directly governs the stress and deformation mode of the support system. When the coefficient reaches 0.15, the maximum deformation of the support piles on the loaded side increases by 90.5%, while the piles on the opposite side deforms outward. The proposed gradient reinforcement method demonstrates both technical and economic advantages for deformation control. Its effectiveness is comparable to the conventional full-area reinforcement method, yet it achieves a 28% reduction in material costs. It can be concluded that the gradient reinforcement scheme demonstrates notable advantages. The research results can serve as a valuable reference for the preliminary design of support structures in similar excavation projects, as well as for the control of overall excavation deformation during the construction phase.