Large-scale Distributed Generation (DG) is connected to the distribution network, and its voltage support capacity can enhance power supply capacity and improve the power quality of the power grid. Three evaluation indices are designed to quantitatively evaluate the voltage support capacity of the DG, containing the low voltage support capacity of DG, the qualified rate of the limited voltage and the limited power loss. The evaluation range of the indices is limited by a power circle to reduce the influence of the nodes outside the range of the DG's power supply capacity on the evaluation indices, and to improve the accuracy and sensitivity of the indices. In addition, an evaluation method of DG voltage supporting capacity based on an analytic hierarchy process is proposed. The calculation of weight coefficient between indices is improved, and the power supply performance of the distribution network is quantitatively evaluated from the three perspectives, containing the low voltage location, power quality and power loss. Then, the discriminant scale is calculated based on the evaluation result, and a comprehensive evaluation result of DG voltage supporting capacity is calculated. Finally, a case study is provided, based on an actual 43-node medium voltage distribution system, to verify the effectiveness of the proposed index and evaluation method. This work is supported by the National Natural Science Foundation of China (No. 51707176), the Science and Technology Project of State Grid Henan Electric Power Company (No. 5217I020000G), and the High School Key Research Program of Henan Province (No. 20A470014).