Abstract: A new method to extend the dynamic range of the magneto-optical current sensor is presented.The magneto-optical current sensor is based on Farada effect and Ampere's law to realize the current measurement.Because the Faraday rotation angle increases periodically with the current measured,only a monotone region of the sinusoid could be used and the measurement range is narrowed.With the wavelength dependence of the Verdet constant,a large current could be measured by wayof measuring the difference of the rotation angles corresponding to the two different wavelengths within one sensor.The metering data,which is more accurate than the data from the dual wavelength.can be acquired by a single wavelength.It is theoretically shown that 20% Verdet constant difference between the two wavelengths will increase the current measuring range 6 times.This method can make the magneto-optical current sensor adaptive to both metering and protection in power system.