The increasing complexity of the grid structure and the variation of the operation mode have a significant impact on the voltage stability of the system，and the traditional voltage control method is difficult to accurately identify the voltage dominant node，which restricts the effective control of the local voltage. In view of this issue，a sub-regional dominant node optimal identification method considering the neighbourhood coupling degree is proposed in this paper. The method is based on a reasonable division of the grid，the sub-regions reflecting the local voltage control characteristics is obtained，and the voltage dominant nodes in each sub-region is accurately located by constructing the dominant node optimal identification model. Firstly，the full-dimensional extension matrix model of electrical distance is constructed through considering the control characteristics of reactive power sources，and the hierarchical clustering algorithm is used to achieve the sub-regional classification of the grid；Then，combining the principle of connectivity of the region，the power-voltage coupling relationship between controllable nodes in the sub-region and adjacent regions is analyzed，and a comprehensive sensitivity index considering the neighbourhood coupling degree is constructed，and the dominant node in each sub-region is identified in accordance with the results of the index calculations. At the same time，the variation of dominant node under different operation modes of the grid is studied to verify the flexibility and adaptability of the proposed identification method. Finally，the IEEE 39 node system is used for simulation analysis. The results show that the proposed method takes the coupling degree of neighbouring nodes into account，and is more reliable than the traditional dominant node selection method. In addition，the method not only adapts to the flexible and variable grid operation mode，but also provides effective support for the reactive power compensation capacity planning of complex networks.