The utility model provides an online positioning system of high tension cable line fault, two current signal modulation terminals are used for being connected to the both ends of treating the detection streamer and carry out electric current signal acquisition to the two circuital current signal modulations that to gather are two way light signals, and two the optical signal input ends of optical fiber transmission to optical path switching unit are connected to two rethreads, microprocessor control optical path switching unit connects the optic fibre switching with two and is connected to the measuring junction of fiber time delay caliber or two current signal demodulation terminals's input, the delay information that optic fibre carries out two connection optic fibre of delay assay acquisition are connected to two of inserting to the fiber time delay caliber to with delay message routing to microprocessor, two current signal demodulation terminals are the signal of telecommunication with the light signal demodulation of inputing, again with sending into microprocessor after the conversion of signal of telecommunication AD. This positioning system can avoid the fiber length difference to bring delay measurement and need not the cable interface and withdraw from the operation, has better market perspective.