The combined atmospheric radiative transfer (CART) has been developed primarily,it is an atmospheric transfer radiative software based on the atmospheric model in regions of China and using particular arithmetic,and can be used to calculate atmospheric spectral transmittance,thermal radiance,scattering radiance and solar direct irradiance quickly,its spectral resolution is 1 cm-1.This paper tests CART′s calculating precision on horizontal path condition by comparing with the horizontal infrared transmittance measured by Fourier Transform mid-and near-Infrared (FTIR).The compared results show that the maximum errors between CART′s calculating horizontal infrared atmospheric transmittance and measured values are less than 0.1,and the standard error is about 0.04.This illustrates that the horizontal infrared atmospheric transmittance calculated by CART is reliable.