Based on gamma fog drop size distribution model and empirical relation of water content and visibility for radiation fog and advection fog, the attenuation due to fog was calculated and analyzed for 10.6μm infrared wavelength. The empirical relations between fog attenuation and water content as well as visibility were derived through regression analysis. The linear relation between fog attenuation and water content for dense radiation fog is in good agreement with available results of experiments and semi empirical formula. Finally, the fog attenuation between 10.6μm and visible wavelength was compared, and the results show that the attenuation at 10.6μm is greater than that at visible wavelength for dense advection fog.