Large-scale wind power integration changes the power flow distribution, line transmission power and transient characteristics of the original power grid. This paper applies unified power flow controller (UPFC) to the wind farm interconnected to circular transmission network model and studies the performance of the wind power grid improved by UPFC. The double closed loop feedback control of UPFC shunt-side converter is used to improve the low voltage ride through capability during three phase short circuit fault of wind power output line. The active and reactive power independent control system of UPFC series-side converter is used to output offset voltage to transmission lines to study the power flow optimization of the wind power integration. The model is built by Matlab/Simulink and the simulation result verifies the improvement of the LVRT capability and the optimization of the power flow based on the reactive power compensation and power flow control ability of UPFC.