Abstract: If the virtual inertia control is implemented in variable speed wind turbines,the inertia control coefficient would become a variable parameter,which tend to affect power system transient stability. Firstly,the equivalent model of interconnected system with wind power variable inertia is derived. Secondly,based on the extended equal area criterion,the influence mechanism of wind power virtual inertia on the power angle first swing stability is analyzed theoretically. By establishing the linearized state equation and using the integral manifold method to achieve model reduction order,the effect of adjustable virtual inertia on the damping characteristic is then analyzed. Furthermore,the regional cooperative control of variable inertia for doubly fed induction generator is proposed to improve the stability performance of the interconnected power system. Finally,a simulation model for interconnecting two power generation areas with a wind penetration rate of 30% is established,and the dynamic simulation results show the flexible virtual inertia can enhance the first swing transient stability,as well as damp the subsequent power oscillation.