In order to research the influence of short circuit fault for metro train traction system on safety performance of the power net, the detailed mathematical model was derived for the short circuit fault of metro in the traction line. Combining with the practical parameters of a subway, simulation analysis of short circuit of filter reactor and traction inverter in metro train was completed with MATLAB. The influence of the fault location on the short circuit current and its change rate was revealed. The simulation results could provide power system security assessment data for the metro companies.