For the purpose of effectively coping with the danger from infrared imaging guided weapons, Directional Infrared Countermeasure(DIRCM) technology is greatly developed in recent years, which has got promising to be the main trend of future Infrared Countermeasure(IRCM) technology. Focused on the research requirement for infrared image-forming system′s performance on the conditon of DIRCM laser′s irradiation, the whole process of DIRCM laser′s interaction with atmospheric environment and infrared image-forming system, including laser′s emitting, lasing atomspheric transmission, optic transmission and detector′s response of the input laser into infrared image-forming system, was well investigated and modeled, upon which the simulation model of infrared image-forming system′s performance under DIRCM laser′s irradiation was built. Finally, the proposed calculation method and simulation model in this paper were demonstrated valid for simulating infrared image-forming system′s real reaction performance to DIRCM laser′s irradiation, which are able to obtain efficient simulation results not only on the DIRCM laser′s infrared imaging grey level, facula appearance and grey texture, but also on the infrared image-forming system′s saturation and damage effects caused by the DIRCM laser′s irradiation at different situations, such as different distances, illuminations, etc. Meanwhile, above results were verified by real experiment which employed laser to irradiate real infrared thermal imaging system, the simulation data were testified close to real experiment datas, the validation of proposed method and model also gets proved. The proposed work provides foundation for further research into DIRCM′s jamming performance against infrared imaging guided weapons.