Radiative heat transfer in a one-dimensional soot/gas mixture is analyzed using the P-l approximation. Results for heat transfer and temperature profile are generated for mixtures of different compositions under the condition of radiative equilibrium. Based on the tabulated heat transfer result, a concept of equivalent absorption coefficient is introduced and demonstrated to be extremely useful in describing the mixture's radiative heat transfer characteristic. Some interesting mathematical properties of the equivalent absorption coefficient are developed and their physical implications are discussed.