The invention belongs to the technical field of photovoltaic power generation, and particularly relates to a photovoltaic power generation unit group equivalent modeling method based on characteristic distances. The method comprises the steps that firstly, all power generation units in a photovoltaic power station are numbered, and inverter parameters in each power generation unit are read; secondly, the trace sensitivity of the inverter parameters in one power generation unit is calculated and a column vector is constituted; thirdly, the characteristic distances among all the power generation units are calculated; fourthly, all power generation units serve as main units in sequence, the sum of the characteristic distances between each main unit and all the other power generation units is calculated; fifthly, the main unit with the smallest characteristic distance is selected as a main power generation unit; sixthly, the inverter parameters in the main power generation unit serve as parameters of a photovoltaic power generation unit group equivalent machine, and the rated capacity of the equivalent machine is modified into the sum of the rated capacity of all the power generation units in a group. The equivalent modeling method is distinct in physical conception and improves equivalent modeling accuracy.