Doubly fed induction generator has become the mainstream model of the modern wind power, however, during the fault, the rotor-side converter is out of operation under the action of the rotor protection, and cannot provide reactive power to the grid to maintain the stability of the system. This paper analyzes the reactive power regulation capability of grid side converter, proposes two control modes of voltage outer loop and power outer loop and constructs three-machine nine-bus system containing wind farm. Simulation results show that grid side converter can produce more reactive power under two control modes compared with the traditional unity power factor control under fault condition, and can improve the system transient voltage stability to a certain extent. Finally it compares and analyzes the reactive characteristics of the grid side converter with two control modes.