The invention belongs to the technical field of cable online monitoring, and especially relates to a device for the online monitoring of a grounding loop current of an urban cable line. The device is high in efficiency, is convenient for power supply and is stable in operation. The device comprises a current collection module, a signal analysis and processing module, a wireless communication module, and a power module. The structural main points of the device are that a cable grounding current signal is connected with a current collection module; the current collection module is connected with the signal analysis and processing module; the signal analysis and processing module is connected with the wireless communication module; the power module supplies power to the current collection module, the signal analysis and processing module and the wireless communication module; the current collection module comprises an A-phase current collection circuit, a B-phase current collection circuit, a C-phase current collection circuit, an N-phase current collection circuit, and an analog-digital converter.