Abstract: The Doppler shift of radio wave echoes reflected from ionosphere is an important parameter to observe ionospheric movements. Generally, high resolution Doppler shift could be obtained in drift mode with digital ionosonde. In this mode, only a few working frequencies are used, so ionospheric disturbance profile with height cannot be acquired. However, in ionogram mode, though Digisonde works with many sounding frequencies, the resolution of Doppler shift is too low to detect ionospheric disturbances precisely. In this paper, a new analysis method is given based on the fact of narrow band of ionospheric echoes, through converting sixteen Doppler channel data to temporal domain by IDFT and estimating the phase differences of adjacent time by least square method, the high accurate doppliono-gram could be acquired in ionogram mode. In order to prove the effectiveness of the method, some experiments have been carried out with Digisonde-256 at Wuhan Ionospheric Observatory. The experimental results have revealed that the high accurate Dopplionogram can be acquired, and the present method is very useful in experimental investigation of ionospheric disturbances.