One of the key areas of advancement in space-based infrared sensing is the high-sensitivity detection of small and weak targets. A major innovation in this regard is the design of the infrared detection system indicator, which is influenced by the characteristics of the target background radiation. The effectiveness of space-based infrared detection is significantly challenged by airborne targets, especially civil aircraft. These targets are active in the upper troposphere and lower stratosphere. They exhibit weak and variable radiation characteristics due to complex background clutter and atmospheric attenuation. Aiming to address this issue, this paper proposes a multi-parameter joint optimization method for an airborne target infrared detection system based on the coupling of the multiple physical effects. Firstly, the initial optimization of the target detection spectral band in the sky is completed based on the spectral radiation characteristics of the target, the background, and the spectral atmospheric transmittance change characteristics of the target-sky-based detection platform. Subsequently, the detection sensitivity requirements are proposed. Then, a system parameter optimization method is established with the target motion speed limit, earth background limit, and detection sensitivity as the three major boundaries. This method facilitates the creation of an infrared detection index system for air targets.