In order to do protection settings and performance analysis for doubly-fed induction generator (DFIG) wind power system, the equivalent circuit of DFIG is proposed in this paper. It has been discovered that there exists a lot of rotor speed frequency component in DFIG short-circuit current, but no equivalent circuit of DFIG has been able to represent that component distinguished from the synchronous component so far. Starting from the instantaneous model of DFIG, equivalent circuits corresponding to the synchronous frequency and rotor speed frequency components are derived respectively according to the characteristics of the two accomponents. Based on the proposed equivalent circuits, the short-circuit current of DFIG can be calculated conveniently. The calculation process is totally independent with simulation, and is proved to be effective by PSCAD simulation. The calculation method proposed in this paper is helpful to relay protection settings and designing.