The utility model relates to a device for measuring a current in a full-scale measuring-range. The device comprises a current sensing system, a data acquisition device, a total control system and a loop selection switch. The data acquisition device is used for sampling a total secondary loop current signal output from the current sensing system and storing data. The total control system is used for accepting a secondary loop current signal output from the data acquisition device. The loop selection switch is used for controlling investment of a branch circuit according to a command output from the total control system. A double-channel power supply system is used for supplying power to the current sensing system. The device for measuring the current in the full-scale measuring-range can be used for measuring a current outdistancing a measuring measuring-range of an internal current internal current sensor, high-precision output in the full-scale measuring-range can be achieved.