In order to cope with the voltage control difficulties of the active distribution network with large-scale flexible load, this paper proposes a distribution network partition method based on improved particle swarm optimization algorithm. Distributed Generation (DG) can actively participate in the control of the distribution network, and introduces four indicators to evaluate the partition, including reactive/active reserve and strong coupling within the region, and the weak coupling between regions. Combined with reactive/active power controllability and voltage observability, the dominant node selection formula is constructed. This method regards the partition process as an optimal problem, so that the partition can be flexibly adjusted according to the DG parameters and the structure of distribution network. The simulation has proved this partition method is scientific and based on which the distributed voltage control can effectively alleviate the problem that the voltage exceeding limit caused by large-scale flexible load. It has practical application value. This work is supported by Science and Technology Project of State Grid Corporation of China (No. 52022316001P).