In recent years, distribution network investment of county-level power supply companies continues to increase. There is a lack of a scientific and reasonable distribution network investment benefit evaluation system. This paper firstly constructs an investment evaluation index system for two-layer distribution network from the aspects of equipment level, power supply capacity, line loss reduction and power consumption increase. Secondly, the weight of each evaluation index is calculated by using analytic hierarchy process (AHP) and entropy method. Thirdly, the correlation of every evaluation index data is reduced by principal component analysis (PCA). Finally, the investment benefits of the distribution network of each evaluation object are ranked on the basis of TOPSIS. This method can be a reference for the superior management unit to evaluate the overall investment benefit in distribution network of county-level power supply company scientifically and reasonably, and then effectively guide the investment plan of distribution network in the next year.