The invention discloses a stability control system of a photovoltaic grid-connected power generation system. The stability control system comprises a photovoltaic array, a DC converter (a boost chopper), a stability control module, an inverter and an AC power grid, and is characterized in that the stability control module comprises a voltage collector, a Buck/Boost bidirectional converter, a storage battery, a data collection and conversion module, a stability controller (a CPU) and a trigger unit of an electronic switching device in the bidirectional converter. Compared with an existing controller, controlled variables in the stability control system also contains the charge state of the storage battery, collection for actual states of the storage battery is more accurate, the Buck/Boost bidirectional converter is adopted by a control circuit, and the electronic switching device adopts an IGBT (insulated gate bipolar transistor) with better performance, so that the stability control system is enabled to be high in control precision, and the output stability of the photovoltaic grid-connected power generation system is ensured.