A current sensor for measuring the inhomogeneity of potential distribution of an arrester having a metal casing, a protection circuit of sampling resistor, a signal conditioning circuit, a signal acquisition circuit, an electro-optical conversion circuit, and a battery module. The signal acquisition circuit includes MSP430F149 micro controller unit having an A/D converter and a serial port. The current sensor is an active sensor, works in a high floating potential, and has a good real time response, high accuracy, low power consumption, good electromagnetic compatibility, and strong anti-interference capability even under harsh electromagnetic conditions.