The invention relates to a position controllable ISAR decoy target image synthetic method. The method comprises the following steps: first step, intercepting and sampling ISAR signals, to obtain a signal phase sampling value signal; second step, according to a decoy target synthesis template, forming an image modulation parameter; third step, according to a modulation position parameter, forming an abscissa modulation factor and an ordinate modulation factor; fourth step, modulating and transferring sampled signals. The method is advantaged in that, first, the modulation method is relatively simple, just scattering intensity of a decoy target scattering point and phase information are needed to be known, second, according to modulating the position parameter, a decoy target image with controllable position can be flexibly controlled.