The invention relates to a power distribution network index evaluating method and a power distribution network index evaluating device. The power distribution network index evaluating method comprises the following steps of 1), establishing a power transmission and distribution network index database and a performance index database; 2), inputting basic data of an electric power amount, an electric power price, a debt ratio limit and a performance index value, and calculating an electric power selling benefit, a loss reduction benefit, a reliability benefit and an energy-saving loss reduction benefit; 3), calculating the comprehensive benefit of a power grid, and calculating power distribution network benefits of different areas based on a benefit distribution coefficient; 4), obtaining a retained benefit, a depreciation amount, a financing amount and circulating assets according to the power distribution network benefits and asset-liability ratios of different areas; and 5), setting a fact that power distribution network investment capability Y comprises the retained benefit, the financing amount, the depreciation amount and the retained circulating assets, and obtaining the investment capabilities Yi of an i-th year of different areas in different voltage grades. The power distribution network index evaluating method and the power distribution network index evaluating device can perform accurate evaluation on the index of the power distribution network.