Abstract: Fundamental frequency and instantaneous phase of grid voltage are critical information for grid-connected power generating systems.The DC-offset of grid voltage sampling signal is not propitious for accurate phase locking.By analyzing the impact of DC-offset on the adaptive notch filter（ANF）,an integrator is added to the ANF to enable it to cope with the DCoffset.Fundamental frequency,amplitude and phase of the single-phase grid voltage signal containing the DC-offset and harmonics are accurately extracted by means of the enhanced ANF,based on which the validity of phase-locking is proved.