We present here a novel method to track and lock the frequency of laser diode using the transmission spectrum of a Faraday anomalous dispersion optical filter (FADOF) as the frequency discrminato. The frequency stability obtained is better than 2.1×10-10 for 100 ms≤τ≤10 s sampling time. And by changing the intensity the intensity of magnetic field from 0.7×10-2 T to 2.2×102 T, we obtained a continuous frequency scan of more than 2 GHz.