Impedance-based method is applied in this paper to analyze the relationship between the converter control system and the stability of DFIG grid connected system. The model of DFIG equivalent input admittance considering the phase error of controller system caused by PLL is proposed. The impact of controller proportional and integral gains is analyzed according to the proposed model. Stability of the DFIG system connected to weak grid can be predicted with the proposed input admittance model using GNC. Simulation results verify the validity of the proposed equivalent DFIG input admittance and the stability analysis.