The reactive power output allocation for generators is an important technical link of automatic voltage control (AVC) system in power plant. The allocation strategy affects the security of the AVC control and operation economy of power plant. In order to improve the profits of the power plant, a reactive power allocation strategy based on the reactive power ancillary services (RPAS) compensation is proposed, and the optimization model is established. The model considers the increasing cost of units and transformer loss when the power plant adopts the RPAS. Under the condition of satisfying the constraints such as the control target of AVC system of the dispatching department and secure operation domain of generators, and taking the maximum profits of power plant as the optimization objective, the model solves the controlling quantity of reactive outputs of AVC generators and then they are implemented by corresponding units. The method is proved to be effective in the simulation and the strategy can satisfy the requirements of voltage regulation and significantly improve the economic efficiency of the power plant.