In large hub city power grids, load centers often lack flexible and continuously adjustable reactive power sources across multiple voltage levels, leading to a “hollowing-out” of power supply. This paper proposes a coordinated two-level voltage control optimization method tailored for such “hollowed-out” power grids. In this method, the high-voltage busbar of all controllable power plants within a region are generalized as voltage-dominant nodes, and regional voltage regulation is achieved by minimizing the sum of squared deviations between the busbar voltages and their reference values. Meanwhile, the coordination relationships among upper-level and lower-level regions are explicitly distinguished, and threshold-based control objectives between hierarchical regions are introduced to improve the reactive power support capability of lower-level areas. The effectiveness of the proposed method for regional reactive voltage control in hollowed-out power networks is verified through simulations using a standard test system combined with actual grid data from China.