In order to research the control strategy of low voltage ride through (LVRT) of DFIG during the asymmetric voltage sag, it is necessary to research the transient characteristic of DFIG during the asymmetric voltage sag. This paper utilizes the transient change mechanism of DFIG stator and rotor flux in the case of single-phase grounding fault, deduces and obtains analytical expressions about stator transient current, electromagnetic torque, output active power and reactive power of DFIG. On the basis of above, the main factors are got which affect single-phase grounding fault electromagnetic transient process. And simulation model of 1.5 MW DFIG during single-phase grounding fault is built on MATLAB/Simulink, the simulation results are closely consistent with the analytical calculation results, which shows the correctness and effectiveness of the analytical expressions derived. Analysis of this paper can provide theoretical basis for control strategy of asymmetric LVRT.