Abstract: The jamming effectiveness of infrared jammer on cross-detector was researched by modeling and simulating. The mechanism of cross-detector seeker's target recognization and the influences of jamming signal on cross-detector seeker were analyzed. The total simulation model of missile and the target recognization models of reticle seeker and cross-detector seeker under jamming were established. By simulation, jamming effectiveness of IR jammer when jamming two representative kinds of IR missiles in different suppression ratios and duty ratios were researched quantificationally. The results show that IR jammer's jamming effectiveness on cross-detector seeker is much worse than it on reticle seeker; suppression ratio's increase can rise IR jammer's jamming effectiveness; the jamming effectiveness on cross-detector seeker reaches to maximum when duty ratio is 0.5.