When the wind turbines with additional virtual inertia are connected to the grid, the transient stability level of the whole system is changed due to controllable inertial time constants. Firstly, the mathematical model of equivalent two-area system with double fed induction generator is derived. According to different operation modes, the influence of variable speed wind turbine’s virtual inertial time constant on interconnected system power angle transient stability level is analyzed. Under the different power angles swinging direction, the relationships between the virtual inertia of wind turbine and the transient stability level of the equivalent two-regional system are discussed, respectively. Finally, the equivalent two-area interconnected system with high wind Penetration is simulated and analyzed. It provides direction for the power system transient stability control with large scale wind farms.