This study establishes a coupled fuselage-nozzle-plume model based on thermal-mechanical coupling mechanisms to analyze jet aircraft infrared characteristics. Numerical simulations reveal that skin temperature under non-afterburner flight conditions increases nonlinearly with Mach number and decreases gradiently with altitude, while nozzle thermal disturbance creates jet-like plume temperature attenuation. The 3–5 μm radiation primarily originates from high-temperature nozzle components, whereas 8–14 μm band exhibits stronger sensitivity to skin temperature variations, demonstrating superior omnidirectional detection potential. Information entropy analysis shows long-wave imaging exceeds medium-wave by two orders of magnitude, attributed to enhanced grayscale uniformity. These findings provide critical theoretical support for infrared signature analysis and detection technology development under complex operational conditions.