Clustering and aggregating the wind turbine generators with similar operation state is common in the wind farm equivalent modeling，which can obtain a multi-machine equivalent model of the wind farm.A more simplified equivalent model can be obtained if wind turbine generators in different operation states can be aggregated with satisfied accuracy.This paper is focused on the equivalent modeling of doubly-fed induction generators（DFIGs）with significant difference in wind speeds.An aggregation method of rotor-side controller of DFIG is proposed.The reference value of the aggregated rotor-side controller will be modified to improve both the steady and dynamic accuracy of the equivalent model.Thus，the aggregation of DFIGs under different wind speeds can be achieved.And a procedure for obtaining a single-machine equivalent model of a DFIG-based wind farm is also proposed.The proposed method brings a new way to build a more simplified equivalent model of the wind farm，which is different from the clustering and aggregation method.A case study is used to test and verify the proposed method.