A method for determining the optical thickness and effective particle radius of spherical aerosols with sun light of a single wavelength is presented. Based on the vector radiative transfer theory, the reflection matrix of the aerosols is calculated by using the adding-doubling method for λ=0.75μm and 3.3μm, the effective radii of aerosol particles were 0.01—1.5μm, and the optical thickness were 0.05—1. We modeled the retrieval process by computer simulation. From the numerical results, we conclude that the radiance combined with polarization is capable of uniquely retrieving optical thickness and effective radius with high accuracy. Especially, when the effective radius is less than 0.4μm, a visible light wavelength can be used for retrieval; when the effective radius is larger than 1.0μm, an infrared light wavelength can be used for retrieval; when the effective radius lies between 0.4 and 1.0μm, both of the two wave bands can be used to obtain a unique result with high accuracy.