With the ever-expanding deployment of renewable energy sources (RESs), the short-time transients have more significant impacts on shaping the characteristics of large power grids. However, the electro-mechanic transient simulation cannot reflect the short-time transients, while the current electromagnetic transient simulation cannot tackle large power systems due to the huge computational burden. This paper presents a novel simplified electromagnetic transient simulation method for large-scale power systems with high penetrations of doubly fed induction generator (DFIG)-based wind farms. Firstly, a DFIG-based wind generator (WG) model is built to simplify the detailed switching process of power electronic devices as well as reproduce external characteristics to the power system. Secondly, an initialization technique is further adopted using the power flow results, aiming to avoid the long and unnecessary computation process for starting the simulation with traditional methods. Finally, a simulation tool is developed based on the proposed method, and a real power system with 9889 buses and 898 wind farms is simulated. Results show that the simulation can start smoothly with good accuracy. Therefore, the proposed method can be employed in electromagnetic transient simulation of large-scale AC power systems with high penetrations of RESs.