Abstract: Using the HITRAN2016 database, a new database of atmospheric molecular absorption coefficients was obtained by recalculating and fitting, which was applied to the upgraded 2nd edition of the Combined Atmospheric Radiative Transfer (CART2). A CART2P1 program module with a spectral resolution of 0.1 cm⁻¹ has been added. Compared to CART 1.0, atmospheric molecular absorption takes into account weaker molecular absorption lines. The comparisons to LBLRTM between the calculated results of MODTRAN5 and CART showed that CART2 can accurately simulate the absorption of atmospheric molecules; the calculated results agree well with the real measured ground-based infrared high-resolution solar spectrum. The atmospheric transmittance and environmental background radiation calculated by CART2 with a finer 0.1 cm⁻¹ spectral resolution can distinguish discrete atmospheric molecular absorption lines, which can be applied to radiative transfer calculations for medium-to-high spectral resolution optical engineering or some laser engineering.