With the increasing of penetration of wind power in the power grid, the impact of wind power on the system stability becomes more and more apparent. Constructing a suitable Double-Fed Induction Generator (DFIG) farm model is the basis for the dynamic study of wind power embedded system. A novel method, based on the single-machine aggregation method and Selection Modal Analysis (SMA), is proposed for the modeling of wind farms in this paper to solve some problems, such as high-order model and long time for simulation. Firstly, multi-DFIGs are aggregated as an equivalent single DFIG. Then, based on the aggregated model, the SMA method is applied to further reduce the model order. The numerical simulation results show that the dynamic equivalent method can not only realize the equivalent of multiple wind turbines under different wind speeds, but also can fit the steady and transient behavior of the system, which can simplify the model and thus improve the computational efficiency. This work is supported by Youth Fund of National Natural Science Foundation of China (No. 51807150) and the Science and Technology Project of Electric Power Research Institute of Guizhou Power Grid Co., Ltd. (No. GZKJXM20171048) “Research on Operation Characteristics of Wind Turbine and Stability of Regional Power Grid”.