The present invention relates to a T-connecting line fault range finding method. The method comprises: determining whether a T-connecting line is a three-terminal operation mode or a two-terminal operation mode or not, and performing fault range finding according to the operation mode of the T-connecting line. When the T-connecting line is the three-terminal operation mode, if faults happen on a certain branch, the voltage and the current correlated to a T node are calculated to employ double-terminal range finding algorithm to obtain the accurate positions of fault points. When the T-connecting line is the two-terminal operation mode, the fault distances between each terminal and the fault points are calculated in the two operation terminals, if the faults happen on the T node or a non-operation branch, the two operation terminals are subjected to single-terminal range finding so as to determine whether the faults happen on the T node or the non-operation branch, and if the faults happen on the non-operation branch, the single-terminal range finding is performed again to obtain the accurate positions of the fault points. Therefore, whatever the T-connecting line is operated in any mode, The T-connecting line fault range finding method can accurately obtain the positions of the fault points to facilitate subsequent fault solution.