Most research on the short-circuit current contributed by wind turbine driven doubly-fed induction generator（DFIG） focuses on the non-grid-connected DFIG and grid-connected DFIG with the short-circuit point located at the generator's terminal. When the DFIG is connected to a distribution network， the short-circuit current of DFIG may be affected by the characteristics of the distribution network， the location of the short-circuit point and other factors. First， based on the Park model of induction motor， a detailed mathematical derivation for the transient characteristics of DFIG in the external fault is conducted and analyzed. The composition of the short-circuit current of DFIG and an approximate expression of the short-circuit current are proposed. Then， the effect factors to short-circuit current of DFIG are analyzed. Finally， the simulation shows the correctness of the analysis.