Jamming technology research of terminal sensitive projectile has important value in military application. On the basis of the working principle and circuit characteristics of millimeter wave (MMW) alternating current radiometer, a novel MMW active jamming method for waveform deception is proposed. In this method the narrowband signal transmitted by the MMW interference source is used as a heat source to obtain a wide time signal through the broadband receiver and detector, then derivative action of the video amplifier low frequency circuit makes the wide time signal to yield a splitting signal of positive pulse waveform and negative one, and the negative pulse of the splitting signal results in the similar signal waveform of the negative pulse in armored target detection, thus realizing the interference effect of cold target simulation. The results for both simulation and experimental data demonstrate feasibility and validity of the proposed method.