A method of longwave radiative transfer parameterization for the Earth's atmosphere is described. Spectral line parameters are used to calculate characteristics of molecular absorption. The k-distribution technique is shown to provide uncertain calculation of the frequency dependence of the transformed coefficient of molecular absorption. So, a phenomenological scheme has been constructed to treat overlapping gas absorption bands, which ensures higher level of parameterization of transmission functions than traditional techniques can provide. In comparison with line-by-line (LBL) techniques, this method calculates the transmission functions along any atmospheric path with an accuracy better than 1-2%.