A dual-channel algorithm is developed to retrieve aerosol optical thickness of cloudless atmosphere over homogeneous underlying surface from the reflectivity data in VIS and NIR bands observed by AVHRR on board NOAA-14. The adoption of the relationship between the aerosol's scattering and wavelength in this algorithm offsets the error in the parameterization of atmospheric factors and underlying surface reflectance when a single channel is used. The significant advantage of the dual channel algorithm is that a retrieving accuracy greater than 90% has been achieved under the condition of homogeneous surface.