The invention discloses a reactive voltage control system for a heavy load time frame of a power grid. The reactive voltage control system is externally connected with an SCADA system, and comprises a topological network establishment module, a collection module, an analysis control module and an output module, wherein the topological network establishment module is used for establishing a power grid topological network according to a power grid model; the collection module is connected with the topological network establishment module and used for collecting and obtaining a reactive value of an electric reactor according to the power grid topological network; the analysis control module is connected with the topological network establishment module and the collection module separately and used for adjusting a capacitor on a bus where the electric reactor is positioned according to the reactive value of the electric reactor, and generating a power grid remote control instruction by combination with the power grid topological network; and the output module is connected with the analysis control module and used for sending the power grid remote control instruction to the SCADA system. By adoption of the reactive voltage control system, the reactive voltage control on the heavy load time frame of the power grid can be realized, and the lowest power loss of the full power grid is achieved.