Based on the principle of FBG sensing mechanism, an alternating current sensor system, which uses a FBG attached on a magnetostrictive rod as the probe,was developed. A dynamic interrogation method was proposed based on wide band light source, by making use of the linear relationship between its power intensity and wavelength as spectrum filter. A 50 Hz AC signal is interrogated successfully through the developed system and the system transfer function was established. The amplitude and fre- quency of the AC signal to be measured can be well deduced through the transfer function of the system, so the alternating current measurement is accomplished.