The operation of the automatic voltage control（AVC）system has greatly improved the reactive power and voltage control feature of the provincial network. However

the top-down open control mode of AVC system is difficult to achieve the overall optimization from theory. On the basis of analyzing the existing control mode of AVC system for provincial dispatching and the automatic voltage control mode in the substation

the joint reactive power optimization of the provincial dispatching and regional dispatching is carried out by adopting the specific control mode of discrete variables in the substation AVC system.With the minimum grid loss and voltage limit as the objective function

power balance and component operating boundary as constraints

a nonlinear reactive voltage optimization model is established and continuous variables and discrete variables are subject to alternative iteration. The iteration optimization for the method and specific adjustment feature of substation is performed and overall optimization can be achieved in theory.The feasibility of the method is verified through a practical example of a provincial power grid.