The invention provides an aggregation equivalent method for a large-scale photovoltaic power generation system based on a structure preserving method. The method comprises the steps of establishing adetailed mathematical model of a two-stage photovoltaic power generation system, wherein the detailed mathematical model comprises a mathematical model of a photovoltaic array, an average model of a preceding-stage Boost circuit, an average model of a backward-stage grid-connected inverter, an equivalent model of a transformer, and mathematical models of a maximum power point tracking controller and a grid-connected voltage and current controller; according to an energy conservation relation among magnetic field energy, electric field energy and generalized potential energy existing in the photovoltaic power generation system, obtaining a relation between state variables the detailed model and an equivalent model of the large-scale photovoltaic power generation system; determining a current and voltage relation between the detailed model and the equivalent model according to the same active power output and power grid access mode between the detailed model and the equivalent model; andutilizing a capacity weighting method, comparing state equations among different models, and providing an equivalent parameter calculation method of an aggregation equivalent model. The method has the beneficial effects that the aggregation model is enabled to reserve the same circuit and control structure as the original photovoltaic power generation system on the basis of simplifying the reduced order model, and meanwhile, an accurate and reliable calculation method is provided for solving equivalent parameters of a photovoltaic array, a Boost circuit, an inverter, an output filter, a transformer, a maximum power point tracking controller and a grid-connected voltage and current controller in the aggregation equivalent model.