The function of DIRCM(Directed Infrared Countermeasures) jamming is to cause the missile to miss its intended target by disturbing the seeker tracking process. The DIRCM jamming uses the pulsing flashes of IR energy and its frequency, phase and intensity have influence on the missile guidance system. In this paper, we analysis the DIRCM jamming effect of spin-scan reticle seeker. Simulation results show that the jamming effect is greatly influenced by frequency, phase and intensity of the jammer signal.