The invention discloses an AVC (automatic voltage control) method and system of a regional power grid. The regional power grid is divided into independent areas with a 220kV substation as a core for AVC; whether AVC of the area is in a 220kV voltage control mode, 10kV voltage control mode or 220kV reactive power control mode is judged according to priority of AVC targets of the regional power grid, and each mode provides corresponding optimization control strategies. With consideration of characteristics and situations of the regional power grid, the dependence degree of AVC on the state estimation result is reduced, coordination control of grid-connected new energy power plants of the regional power grid and reactive resources of the substation is realized, the control ability of the grid-connected new energy power plants is fully played, the action times of switch equipment are reduced to a certain extent, and the method and the system are built on the basis of conventional AVC systems and are convenient to implement.