The solution for the infrared radiation characteristics of the tail flame gas exhibits stronger spectral selectivity and volumetric participation compared to the infrared radiation from the skin. The absorption of asymmetric polyatomic gas molecules demonstrates significant spectral selectivity. Consequently, prior to analyzing the infrared radiation characteristics of the tail flame, it is essential to determine the fundamental physical properties of the gas medium, such as the spectral absorption coefficient, spectral scattering coefficient, and spectral transmittance. Typically, the tail flame plume of an aeroengine consists of H₂O, CO₂, CO, and common atmospheric molecules. Since the infrared radiation of symmetric diatomic molecules can be disregarded, only the absorption and emission of H₂O, CO₂, and CO molecules need to be considered. In addition to these molecules, the infrared radiation characteristics of the aircraft are also influenced by the high-temperature walls of the exhaust system. In this case, both the emitted radiation from the high-temperature wall and its diffuse reflection characteristics must be considered. Calculating the spectral physical properties of the tail flame medium represents the primary challenge in determining its infrared radiation characteristics.A solution method for the radiation transfer equation that combines the apparent ray method and the reverse Monte Carlo method has been proposed. The combined method has the advantages of both methods and can quickly solve the radiation transfer equation for absorption and scattering media. Combined with the statistical narrow-band k-distribution model, the influence of different gas basic physical property libraries on the infrared radiation characteristics of the exhaust system was calculated and analyzed. Considering the existence of multiple versions of HITRAN/HITEMP database, systematic comparison was made between HITRAN database and HITEMP database for solving basic physical properties of gas radiation (Fig.3), and the influence of database version on solving absorption coefficient and radiation intensity was analyzed. The mean absorption coefficient and spectral radiation intensity of single molecule Planck are calculated by using the database, and the absolute errors of the calculated results of each physical property library are calculated relative to HITRAN2020 (Fig.5-7). The results show that the absolute errors of CO₂ molecules exist near three absorption peaks in the bands of 2.7 μm, 4.3 μm and 8-14 μm. The absolute error of CO molecule almost only exists around 2100 cm^-1 wave number. The maximum absolute error of the absorption coefficient of H₂O molecules at a wavenumber of 150 cm^-1 is 0.024 (Fig.11-13). This is because the wavenumber of 150 cm^-1 is far from the emission center of the Planck function. Finally, the accuracy of the proposed method was evaluated based on the experimental results (Fig.17-20).Considering the existence of multiple versions of the HITRAN/HITEMP databases, a systematic comparison was performed among various versions of the HITRAN and HITEMP databases to address the fundamental physical properties of gas radiation. The impact of database versions on the calculation of absorption coefficients and radiation intensity was thoroughly analyzed. Given that the HITRAN database lacks spectral line information for CO molecules in the 8-14 μm band, if the partial pressure of CO in the high-temperature gas under consideration is relatively significant or the calculation results are highly dependent on CO, it is recommended to use the HITEMP database for calculations. The absolute errors of Planck-mean absorption coefficients and spectral radiation intensities of single molecules calculated using the HITRAN2008, HITRAN2012, and HITRAN2016 databases relative to HITRAN2020 were evaluated and compared. Results demonstrate that for CO₂ molecules, absolute errors occur near the three absorption peaks in the 2.7 μm, 4.3 μm, and 8-14 μm bands; for CO molecules, absolute errors are predominantly observed near the wavenumber of 2100 cm^-1; and the spectral line information of H₂O molecules has undergone substantial changes, affecting both the relative magnitude of absorption coefficient values and their distribution across different wavenumber positions. Considering that the infrared radiation characteristics of the exhaust system are influenced by both absorbent gases and diffuse-reflecting solid boundaries, a novel method for solving the RTE was developed by integrating the apparent ray method with the reverse Monte Carlo method. The performance of this method was assessed in an experimental setting. Results confirm that the proposed method can more accurately predict and analyze light transmission issues in complex environments.