Aiming at the low detection probability of airborne infrared search tracking system in combat,a conception of effective detection area is put forward and the models of effective detection area are built in level and pitching angle. Then,the changes of the model with detection probability,operating range,atmospheric transmittance and flight speed are discussed. The simulation results show that the detection area changes with these four factors in real-time,and when the operating range exceeds one hundred kilometers,the weather is bad and flight speed is low,the effective detection area is only a small area above the end of the target. According to the change rule in the paper,the airborne infrared search and tracking system can improve the detection probability through establishing dynamically the function relationship between detection threshold and complex factors. This study provides a theoretical reference for the operational performance of the airborne infrared search and tracking system.