The invention relates to a modeling method for the dynamic equivalent impedance of a large-scale photovoltaic power station, which comprises the following steps of: 1. firstly establishing an integral mathematical model of the photovoltaic power station, wherein the mathematical model comprises the following four parts: a photovoltaic array module, a direct current chopping module, an inverting module and a grid connecting module; cascading the four parts to finish the dynamic equivalent impedance mathematical model of the large-scale grid-connected photovoltaic power station; and 2. obtaining the equivalent impedance characteristics of a photovoltaic assembly according to illumination intensity R (W/m<2>), ambient temperature Ta (DEG C) and the short-circuit current Tsc, the open-circuitvoltage Uoc, the maximum power point current Im and the maximum power point voltage Um of a photovoltaic cell unit in a standard working state, and dynamically outputting the equivalent impedance of the large-scale photovoltaic power station and a dynamic equivalent impedance curve under the same input parameter in real time along with the change of the illumination intensity and the temperature to be directly used for the tidal current computation and the short circuit computation of a power grid at an electric power system area containing the photovoltaic power station.