In order to effectively measure the management level of regional power grid construction and quantitatively evaluate the regional reliability level differentiatedly, a method for evaluating the reliability level of distribution network power supply based on GRA-K-means++ algorithm is proposed. Firstly, both external factors and power grid factors are taken into account, the set of reliability influencing factors of regional distribution network is constructed. The correlation between reliability influencing factors and power supply reliability is analyzed based on grey relational analysis （GRA）, combined with the regional power supply range. Next, the regional weighted clustering model is proposed based on the external factors, the information entropy and correlation with reliability of external factors are used as the index comprehensive weight, and the weighted K-means++ algorithm is combined to cluster the regions with the same external conditions. The reliability deviation index is proposed as the evaluation index of regional reliability level. Then, based on the reliability correlation degree of power grid factors, the key factors leading to low regional reliability are identified, and the direction of construction and management for improving the reliability of power grid is put forward. The algorithm is verified by actual distribution network data, and the results show that the proposed method can effectively realize the reliability level evaluation of distribution network, and provide a certain theoretical basis for decision about reliability improvement methods.