As the transmitting signal of inverse synthetic aperture Ladar(ISAL)has the characteristics of short wavelength and large bandwidth,its echo signal is highly sensitive to the motion of target,which makes its characteristic distinct from the conventional ISAR signal.The precise model of ISAL echo signal is established,the motion-induced effects such as envelope magnification,inner-pulse Doppler and inter-pulse Doppler of the echo signal are analyzed,and the approximation methods as well as the constraint conditions of the three effects are presented.Simulations have been performed to analyze the impacts of envelope magnification and inner-pulse Doppler to ISAL imaging under different motion parameters.Results show that the two effects lead to defocus of the ISAL image,which should be compensated in imaging.