The paper analyzes the theory of generating short circuit current during three-phase fault to research the low voltage ride through (LVRT) control of doubly fed induction generator (DFIG). The approximate analytical expressions of short circuit current are given in the condition of no load and synchronous speed to simplify the analysis. Based on this, the influences of different pre-fault conditions, such as reactive power, active power and speed, on short circuit current of DFIG are studied. At last, a 3MW DFIG model is built and the simulation is done to validate the theory analysis.