The invention discloses a large-scale photovoltaic power station reaction voltage control method. The control method comprises the following steps: detecting voltage at an integration point in real time, comparing the detected voltage with a reference value to automatically acquire and maintain reactive demanded quantity required for the voltage at the integration point through a PI controller, thereby realizing the dynamic regulation on the voltage at the integration point. According to the invention, the relation between the reactive power and the voltage is represented by using an analysis method of the sensitivity so as to provide the design process of the PI controller parameter, and the reactive power optimizing problem taking the uniform in-station voltage distribution as a target is translated into a non-linear planning model with a constraint condition and capable of fast and accurately solving; the reactive power reference quantity of each group of photovoltaic generating unit can be computed by solving the model so as to regulate the reactive power output of each photovoltaic generating unit in real time; on the basis of guaranteeing the stable voltage at the integration point, the in-station voltage distribution is improved, and the stable operation of the photovoltaic power station is guaranteed.