Infrared(IR) guided heat-seeking missiles uses IR emissions from aircraft to detect and track a target. Due to passive characteristic of the IR guidance, early detection of the missile is difficult and it is significant threat to aircraft survivability. Therefore, IR signature prediction of the aircraft is an important aspect of the stealth technology. In this study, we simulated IR signature of the aircraft in real atmospheric conditions. Aircraft surface temperature distribution was calculated by using RadthermIR code. Based on temperature distribution, IR radiance and BRDF(Bidirectional Reflectance Distribution Function) image were simulated for different weather(seasonal) and background(sky/soil) conditions. The IR contrast tendencies are not aligned with surface temperature or magnitude of target IR radiance. Therefore, it is essential to simulate IR signature with various conditions and background to acquire reliable database.