Parallel connected double-track-lines based auto-transformer(AT) is a common way to supply power to high-speed railway (HSR). The distribution of current and its relation with the current of fault site are formulized for different faults. A method to identify fault type and its direction base on the comparison of the virtual values at Traction Substation, AT Post and Subsection Post is proposed for various faults. The proposed method combines the principal of "AT neutral current ratios", which is effective to identify fault's type and direction accurately which is valuable for power supply restoration.