Abstract: Inverse synthetic aperture radar (ISAR) imaging of nonuniformly rotating targets and maneuvering target are difficult but important in ISAR technique. The traditional Range-Doppler (RD) method hardly achieves good imaging results in this case. In this paper, we firstly analyze the radar echo signal model of ISAR. Then we present a new technique based on Radon-Ambiguity transform (RAT) for ISAR imaging upon the signal corresponding to each scatterer of the target is the linear frequency modulation (LFM) signal. Finally we use computer simulation to illustrate its performance and the simulation results show its effectivity.