Abstract: In view of the prevalent safety hazards in early-stage 10kV box-type substations, such as equipment aging, insulation deterioration, and deteriorating operating environments, as well as the practical challenge of high costs associated with complete replacement, this paper investigates how to strike a balance between safety enhancement and economic feasibility under limited budgets. By establishing a multi-dimensional health state quantification assessment system (HHI) encompassing the equipment itself, operating environment, and historical performance, the aging patterns and root causes of risks are accurately identified. Building upon this, the study systematically proposes four differentiated retrofit strategies: complete replacement (S1), partial replacement of key equipment (S2), addition of prefabricated cabin modules (S3), and vertical capacity expansion (S4). To enable scientific comparison and selection of solutions, this research integrates Life Cycle Cost (LCC) analysis and a Security Enhancement Index (SSI) to construct a comprehensive decision-making model centered on "Cost Per Security Improvement (CPSI)", employing fuzzy multi-attribute decision-making methods for strategy optimization. Case analysis demonstrates that differentiated retrofit strategies can achieve over 80% of the safety enhancement benefits at only 30%-60% of the cost of complete replacement, highlighting significant cost-effectiveness.This paper develops a complete methodological framework covering condition assessment, strategy comparison, and decision support, providing a scientific basis and practical guide for power grid enterprises in the refined and economical retrofitting of aging box-type substations.