Abstract: The short circuit current calculation is an important foundation for planning and protection of distribution grid with distributed generation. The transient characteristics of induction generator (IG) are investigated when the unsymmetrical fault occurs in the distribution network, and the analytic formula of its stator current under unsymmetrical short circuit is derived. The impact of an IG rotor speed and the fault initial time (or phase) to the short circuit current under unsymmetrical fault are studied when the short circuit occurs. According to the equation of rotor motion and its steady-state circuits in the positive and negative sequence component networks, an evaluation method to determine the current peak of unsymmetrical short circuit for an IG in distribution grid is proposed by considering its rotor speed variations. The correctness of the method is verified by using the fifth electromagnetic transient model of IG in PSCAD/EMTDC simulation software.