Considering the problems of voltage fluctuations of weak connection wind farm, through the analysis of DFIG’s power flow and derivation of the stator and grid-side converter’s power limitation, the paper proposes a reactive power hierarchical control strategy that compensates reactive in priority when voltage drop, based on traditional reactive power control modes. The reactive power hierarchical control strategy chooses appropriate DFIG units according to the level of voltage fluctuations. That takes advantage of capability of DFIG reactive power, and saves the investment of the low-frequency reactive compensation device. Finally, the simulation model of small scale wind farm connecting to gird is built based on PSCAD/EMTDC simulation platform, the results prove that the proposed control strategy is effective.