With the increasing proportion of renewable energy and the decreasing installed capacity and operating hours of thermal power units, the phenomenon of "hollowing out" of power supply in load centers of power grids in large hub cities is becoming more and more prominent, which brings new challenges to regional reactive voltage control of secondary voltage. Therefore, a coordinated secondary voltage control optimization method is proposed for the "hollowing out" power grid. Compared with the existing research methods, the new method has the following characteristics: (1) The high-voltage busbar of all controlled power plants in the region is generalized to the voltage dominant node, and the goal is to minimize the square sum of the deviation between the high-voltage busbar voltage and its ideal voltage to achieve the optimization of the secondary voltage control; (2) The coordination relationship between the level and the upper and lower levels is distinguished, and the coordination variables of the threshold reactive power and threshold voltage between the upper and lower levels are added as well as the ideal deviation control objectives. The new method improves the secondary voltage control effect of the power supply "hollowing out" load center network through the generalization of the leading node and the coordination of the reactive voltage of the upper and lower regional gateways. Finally, the effectiveness of the proposed method is verified by simulation with the standard example combined system and the actual data in China.