Abstract: The difference of the image generated by real target and Digital-Image-Synthesiser（DIS） is analyzed.Then two methods are deduced to recognize deceivable jamming generated by DIS.One is the uncontinuity of the false target in cross section（Doppler dimension） which is caused by the quantization of phase increment，and the other is the changing number of the target in the imaging field after ISAR processing when the Pulse Repetition Frequency（PRF） of the DIS is unmatched with the opposed radar’s PRF.With the two methods，the limitations of DIS deceivable jamming are found，and the false targets generated by DIS are effectively recognized.