The relative advantages of fluxgate sensor applied to the geomagnetic navigation system were discussed by comparing its performance index with that of the commonly used magnetic sensors.The basic principle of the fluxgate sensor was analyzed.Then Nyquist sampling theorem was used to verify the feasibility of the fluxgate sensor applied to the subsonic low-altitude aircraft by spectrum analysis to the measured magnetic anomaly data in a county.A frequency response indicator was proposed for applying to the subsonic low-altitude aircraft i.e. when the response frequency of fluxgate sensor reach 40.8 Hz to 68.0 Hz it will be able to satisfy the response frequency requirements.