The invention provides a petroleum pipeline cable inquiry unit. The petroleum pipeline cable inquiry unit comprises a light source module, a reflecting module, photoelectric detecting equipment and a signal processing module, wherein the light source module is used for inputting coherent light to a first end of a communication cable; the reflecting module is connected with the light source module through a second end of the communication cable, and used for reflecting the coherent light; the photoelectric detecting equipment is connected with the first end of the communication cable and used for receiving the coherent light signal and converting the coherent light signal into an electric signal; the signal processing module is connected with the photoelectric detecting equipment and used for demodulating the reflected light signal. The petroleum pipeline cable inquiry unit can be used for demodulating an interference signal returned by a michelson interferometer consisting of the equipment and the communication cable according to the laser interference principle and the elasto-optical effect, extracting out vibration information, realizing checking cable router, and giving visual display or audio output.