Abstract: Wind turbines with additional frequency control respond to the dynamic behavior of the grid and have some impacts on the dynamic behaviors of the system. This paper analyzes the changes of the transient characteristics of power system based on the Center of Inertia(COI) theory when large-scale doubly-fed induction generators(DFIG's) with additional frequency control system are integrated to the grid. And the rotormotion equation of the synchronous generator at COI is deduced. Secondly, based on the DFIG's operation characteristics, the capability of the DFIGs response to system dynamic behavior is analyzed. From the above analysis, the influential factors are given on the transient stability of the system integrated with DFIGs with additional frequency control. Finally, IEEE 3-gen 9-bus system model with DFIGs is built in PSASP and the theoretic conclusions are verified by simulation results.