In conventional inverse synthetic aperture radar (ISAR) imaging of complex moving aircrafts, a micro-Doppler effect is generated because of the high-speed rotating parts such as propellers. The rotational parts introduce a sinusoidal frequency-modulated (SFM) signal in the radar echoes, which can significantly affect the quality of the ISAR imaging. To solve this problem, the Doppler frequency forms for the rigid body and rotating parts of an aircraft are analyzed, and a method based on the discrete sinusoidal frequency-modulated transform (DSFMT) is proposed. The SFM signal can be transformed into the DSFMT domain, and the parameters can be estimated by the global maximum. The rigid body is separated after removing the SFM signals using successive elimination technology. This method is not only applicable to targets in uniform motion but also to those in accelerating motion. The results of simulations and a measured data test are given to verify the effectiveness of the proposed method.