The model of wind farm is the foundation of the grid operation and control with wind farm integration. Establishing mathematical models to describe the steady-state and dynamic behavior of large-scale wind farm is a critical issue with tens of millions kW wind power being injected into the grid one after the other. The research of wind farm modeling is analyzed and summarized from four aspects which are wind speed-output power characteristic model, power flow calculation model, dynamic model and transient model; the concept and the necessity of the cascading dynamic process of the wind farm are proposed aiming at the cascading trip-off of large-scale wind farm recently. The problems of large-scale wind farm modeling and further research are pointed out based on an overview of the existing approachs of wind farm modeling.