The utility model discloses a background interference signal detection device for a live power distribution cable. The background interference signal detection device for the live power distribution cable comprises a background interference signal detection device body, TEV sensors and a detection host. The TEV sensors are in communication connection with the detection host through a signal cable. The background interference signal detection device body receives external interface noise signals in a transformer substation and transmits the external interface noise signals to the detection host for processing. The background interference signal detection device body comprises a noise monitoring body and an insulating shell. The noise monitoring body is wrapped in an insulating shell, made of metal and used for receiving external interference noise signals of the transformer substation. The insulating shell completes the insulating and supporting functions. The TEV sensors are mounted outside a switch cabinet and outside the insulating shell of the background interference signal detection device body. According to the background interference signal detection device for the live power distribution cable, the consistency and the synchronism between background noise and actual discharging signals can be guaranteed, and accurate data are provided for historical trend comparison, transverse comparison and fault diagnosis.