The electromagnetic transient process under the grid voltage swell was analyzed by Laplace transform. The stator current contained not only the DC component but also the AC component. The results of simulations spectrum verified the correctness of the theoretical analysis. Different from the conventional research only on the rotor voltage equation considering the dynamic changes of stator flux, while ignoring the influence of the outer power, the stator flux dynamic changes of active and reactive power decoupling effect was analyzed. The improved control strategy considering the influence of stator flux linkage dynamics on the power output loop was proposed. And then, the requirement of reactive current support for unit considering the grid specifications, the grid side converter was controlled to output reactive current, which matches the surge margin and grid voltage quickly recovery. The simulation results showed that the proposed control scheme was capable of not only ensuring continuous operation of the DFIG system during the grid voltage swelling conditions, but also satisfying reactive current output requirement, which achieves the high voltage ride through.