To　track　the　frequency　of　power　system　signals　under　noisy　and　harmonic　circumstances　quickly　and　precisely,　a　reliable　phase　difference　algorithm　based　on　discrete　Fourier　transform　and　its　key　module　implementation　arc　introduced　in　this　paper.　By　utilizing　main　spectral　line　phase　difference　of　two　adjacent　data　windows,　the　frequency　can　estimate　easily.　The　introduced　algorithm　is　suitable　for　FPGA　implementation,　and　the　simulation　result　shows　that　it　has　high-accuracy.