With the scale of wind farm increasing, modeling for each turbine in wind farm will lead to excessive computing, which is not conducive to the research of large-scale wind farms. Wind farms need to be simplified. Firstly, the modeling of doubly fed induction generator and direct-drive permanent magnet synchronous generator which are frequently used currently is summarized. Meanwhile, the methods of dealing with the wind farm in load flow calculation are introduced. Then the aspects of wind power system equivalence are described which include wind speed equivalence, clustering of wind farms, equivalent method of the same group of wind turbines, widely used parameter optimization algorithms and the effect of those optimization algorithms on equivalence. Finally, the commonly used equivalent methods of wind farms composed of single mainstream wind turbine type are reviewed, and the research necessity and trend of the mixed wind farm equivalent modeling with the increasing of amount of the large wind farms composed of different types of wind turbines are pointed out.