Sky luminance distribution is the basis of daylighting, and the reference sky classification is a prerequisite for determining the distribution of the sky luminance. Combining with the daylighting observation data of 1 minute in IDMP daylighting observation stations in Chongqing, by analyzing meteorological parameters affecting the sky brightness distribution, the meteorological parameters, such as the cloud cover, surface conditions on the sun, and the horizon to the zenith luminance gradient, are identified as key factors exerting influence on reference sky classification. On this basis, the reference sky is divided into six types.