Abstract: The incoherent scatter radar(ISR) is a main tool for monitoring the ionosphere on the ground, and can also be used to detect the space objects. When the signal to noise ratio is a bit high, only one pulse is needed to detect the space object and the coherent integration is unnecessary. There usually exist many phase flips in the radar phase-modulated pulses. When the echo pulse with phase flips is filtered by the receiver, the resulting phase flips are not sharp but consist of many slopes. By investigating the echo amplitude variation within this slope, the time difference between the transmission and reception sub-pulse and then the range measurements are known. Then all these range measurements during one pulse are applied to a weighted least-square fitting, which gives the range and its error estimation. By analyzing the EISCAT raw data, it is found that the range error is about several tens of meters, which is far better than that from the frequently-used method based on time difference between the transmission and reception pulse.