Many wind and hydropower stations are connected to the grid in mountainous areas, which brings excellent reactive power resources to the grid in the mountainous areas. The traditional regional optimization control method of Automatic Voltage Control (AVC) relies on state estimation data. The state estimation data of the grid in the mountainous area cannot frequently meet the real-time control requirements. The traditional AVC regional optimization control method can not be implemented generally in the grid in the mountainous area. Moreover, these wind and hydropower reactive power resources can not play an effective role. As a result, the voltage control of the grid in mountainous areas is difficult, the voltage qualification rate is low, and the power loss is high. To solve this problem, this paper proposed a novel regional optimization control method of reactive power & voltage for the grid in the mountainous areas based on the existing AVC system. It does not rely on state estimation data. According to the mountainous area grid's different voltage and reactive power control objectives, the corresponding optimal control strategy is presented and sorted by priority. An accurate selection method of 10 kV bus voltage control target value is proposed and the control target value of 10 kV bus voltage is corrected periodically according to the station voltage in the power supply area. The feasibility and effectiveness of the proposed method are verified by the practical application of a typical mountainous power grid. Without relying on the state estimation data, the proposed method can significantly improve the voltage qualification rate of the applied mountainous power grid, reduce the power loss of the grid and, provide a large amount of reactive dynamic support power as well.