The invention discloses an automatic voltage control method for unified hierarchical coordination of a power grid. On the basis of an energy management system, three-dimensional prediction of a node load is realized by using a three-stage control mode and a decomposition-coordination global closed-loop control mode; the change rule of passive voltage of a power system is analyzed by adopting a systematic passive optimization technology; and according to the top-down control method of the power system scheduling, implementation is realized according to hierarchy in region, partition in layer and hierarchy in time domain. The invention provides a design idea for engineering practice of a unified automatic voltage control system of the power grid and provides a technical support for safe, economical and high-quality operation of the power system.