An automatic voltage control（AVC） system for a large regional power grid is designed and implemented in North China Power Grid. The following new works are reported in this paper: an automatic voltage control mode for regional power grid based on a direct closed-loop control for its own area coordinated with lower-level control centers; an automatic control for 500 kV substation by coordinating with capacitors， reactors， OLTCs and synchronous condensers; a coordinated-control between power plants and substations by online modifying their own constraints; coordination of AVC system with the online security early warning system to ensure static voltage stability; 3-D visualization. This AVC system has been put into real time operation and an excellent performance of the AVC has been observed.