According to the current influence of temperature changes on the detection range of airborne infrared search and tracking (IRST) systems, the changes of target and background radiation contrast, atmospheric transmittance, optics, and detector performance with temperature in the detection process of the system are modeled and analyzed. Based on this, the idea of dynamically setting of the threshold noise ratio according to the temperature change is proposed, and the specific setting algorithm is given. The detection probability envelope under the optimized threshold-to-noise ratio and the traditional constant threshold-to-noise ratio conditions is further simulated and compared, and the results show that he detection envelope of the former increases significantly, indicating that the method of setting the threshold-to-noise ratio according to the temperature can significantly improve the detection performance of IRST.