The invention discloses a control method for improving the voltage stability of a power grid of a large-scale photovoltaic access area. The control method comprises the following steps that: firstly, a regional power grid is equalized to a simple two-node system; for the simple two-node system, original equivalent impedance and photovoltaic impedance at a power supply side are considered, and an impedance function of a photovoltaic system at a load side is considered, and a modulus of impedance is adopted to represent a static voltage stability margin index; and the photovoltaic system is regulated according to the static voltage stability margin index so as to improve the voltage stability of the regional power grid. With the control method adopted, further improvement of the voltage stability of the power grid of the large-scale photovoltaic access area can be realized without additional devices adopted.