In order to solve the problem that the efficiency of chaff jamming pulse Doppler (PD) radar seeker is reduced due to the excessive Doppler frequency difference between chaff and target aircraft under some countermeasure situations, active and passive cooperative jamming mode is adopted to make chaff cloud have Doppler frequency characteristics similar to that of the target aircraft. Based on the principle of active and passive cooperative jamming, the influence factors of active irradiation signal modulation frequency are researched to give the frequency modulation law of the signal under different attack situations of missiles.