Abstract: A coordinated optimization method for voltage regulation and loss reduction in distribution networks(DN) integrated with large-scale distributed photovoltaics(PV) is proposed to address issues of voltage violation and increased network loss based on energy storage system(ESS) configuration. Firstly, a node similarity matrix based on comprehensive electrical distance is constructed. The K-medoids clustering algorithm combined with the modularity index is applied for ESS siting based on DN partitioning, which is aimed at voltage regulation and loss reduction. Secondly, considering PV reactive power control and ESS active power control, a bi-level optimization model for DN planning and operation is established. A multi-objective optimization model of ESS capacity considering ESS costs, DN benefits and PV-ESS user earnings is formulated in the upper level, while a distributionally robust optimization model of network operation is established in the lower level. Thirdly, the proposed model is solved with improved non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ) and alternating direction method of multipliers(ADMM). Finally, the effectiveness of the proposed method in reducing network loss and regulating voltage is validated by two case studies of a distribution line in Shandong Province and the modified IEEE 123-node system.