The problem of small signal stability caused by large-scale wind turbines connected to the power system attracts a lot of scholars' research interest. In order to reduce calculating burden, based on the method of eigenvalue analysis, the article discusses the structure characteristics of doubly-fed induction generator (DFIG), and proposes a simplified method. By this way, the pitch angle and the electrical control model is thus simplified. The resultant simplified model of doubly-fed wind turbine is suitable for studying the influence of wind turbines on small signal stability for low frequency range. The tests on four machines-two areas system are conducted and the results demonstrate the feasibility and effectiveness of the proposed method.