Based on the sky luminance distribution information obtained by the measurements of a camera image system developed by Y. Guangxuan, et al., the authors propose a sky model that comprises the CIE clear sky, pseudoclear sky, pseudo-cloudy sky, and the CIE cloudy sky, according to the sun-disk condition and the thickness of the clouds in the sky. Using fuzzy mathematics, this paper verifies that the proposed model is both reasonable and feasible.