A RX power flow model is set up using the FORTRAN language. Via data exchange， the RX model and the power flow model in PSASP/UPI are alternately solved to obtain the bus voltage and power flow in the system. Using the PSASP/UD module， wind turbine's model， gear box's model and third-order induction generator's transient model are constructed. Based on the models above， three large wind farms， i.e.， Anxi， Yumen and Changma connected to the Gansu Power Grid are modeled. Analysis results of power flow， fault level， peaking demand dispatch and transient stability demonstrate that the proposed model is accurate， practical and effective.