Considering the influence of the aberration of laser system, the atmospheric turbulence, the pointing error of the tracking equipment and the jitter error of the laser axis, the parameter of the power density on the target is used to evaluate the high power laser jamming effect on the infrared imaging guidance system. Combined with the dazzle threshold of the detector, the method for estimating operating range of high power laser system is proposed. The infrared seeker of missile under high power CO2 laser irradiation is taken as example, and the relationship between operating range and laser transmitting power are calculated. The results show that the operating range increases along with the increasing of laser transmitting power, and its curvilinear tread becomes slower as the laser power reaches higher. Besides,the jamming effect of normal incidence of the laser is better than the non-normal incidence.