Abstract: To reasonably evaluate the actual input-output level of medium-voltage electricity business expansion projects in a power grid, this paper takes 450 such projects commissioned in a certain power grid in 2023 as examples, introduces full-cost accounting to construct an evaluation model, and systematically reviews the investment returns of different types of projects. The results show that 80% of the revenue of the regional power grid comes from supporting projects for the 20% of customers that are large industrial users. The average payback period of industrial electricity business expansion projects is approximately 2.8 years, whereas that of public utility supporting projects is 12.6 years, showing a significant difference in returns. Based on these differentiated findings, this paper proposes an optimization scheme of targeted investment and hierarchical differentiated management to improve resource allocation efficiency across the power grid and enhance its overall long-term investment benefits.