Abstract: As the first part of this two-part paper, this paper aimed to theoretically analyze the impact of large-scale wind farms consisted of doubly-fed induction generators（DFIG） centralized integration on transient angle stability of power systems. Firstly, a simplified DFIG model suitable for transient angle stability analysis was put forward according to the transient characteristics of DFIG and the feasibility of adopting the DC power flow method to judge how the wind power penetration influenced the transient angle stability was discussed. Secondly, based on the simplified DFIG model and the DC power flow method, the impact on the transient stability of power systems caused by DFIG integration was analyzed using the extended equal area criterion and a criterion was proposed to judge whether the wind power penetration was beneficial to the power system transient angle stability or not. Finally, simulations on a two-machine system were carried out. The results obtained demonstrate the high accuracy of the proposed criterion.