The invention discloses a device and method for determining the currents of an electrolytic cell cathode plate. The device is arranged on a to-be-detected electrolytic cell. The to-be-detected electrolytic cell comprises a plurality of serial-connection structures which are parallelly arranged. Each serial-connection structure comprises current-entering-side current-sharing bus, a first conductiverod, an anode plate, an electrolytic solution, a cathode plate, a second conductive rod and current-discharge-side current-sharing bus which are sequentially connected. The device corresponds to eachserial-connection structure. The device comprises a measuring box and a single-chip microcomputer, wherein a plurality of magnetic induction sensors are arranged in the measuring box, and the single-chip microcomputer is connected with the magnetic induction sensors; the working faces of the magnetic induction sensors are located on the same plane, and the plant is vertical to the upper surface of the second conductive rod and the magnetic lines of a magnetic field generated by currents on the second conductive rod. By the device or method, the measuring accuracy of the currents of one optional cathode plate in the electrolytic cell can be increased, and measuring errors can be reduced.