This paper establishes a dynamic model for wind turbine-generator unit， including the wind-turbine and asynchronous induction generator. Based on the proposed dynamic model， a model of wind farm connected with an infinite system is constructed. Based on the DC voltage control as well as the feedback control of reactive current， a new control algorithm is presented for STATCOM. Considering three cases， i.e.， the wind speed ramp， the wind gust and the wind disturbance， the numerical simulations on compensation characteristics of STATCOM are studied. The compensation effects between TCSC and STATCOM are compared. The simulation results illustrate that STATCOM can track the changing of reactive power quickly and stably in the procedure of reactive power compensation comparing to TCSC， and there are no serious inrush currents or over-voltages.