The returned signal of low-attitude flying targets is often jammed by the strong ground clutter, so it is a difficult problem to eliminate the clutter effectively. Then, cancellation is a simple and valid method of eliminating the ground clutter. In the paper the cancellation of ground clutter in ISAR imaging of frequency-stepped chirp radar is presented. The identical amount of stretching time-delay with the adjoined bursts of echo is applied in the signal stretching process, and then the ground clutter is filtered by cancellation. After cancellation the coherent signal can provide useful data for the successive ISAR processing. Simulation results show that the proposed method is robust and effective, hence, it is a valuable approach to ISAR imaging of low-attitude flying targets.