For the spectral detection of weak targets in space in daytime, the spectral radiation characteristics of not only the target itself, but also the skylight background surrounding the target must be known. In this paper, Lowtran software is adopted to analyze the spectral radiation characteristics of the skylight background, and a skylight background measurement equipment is developed to detect the real spectral radiation characteristic of the skylight background in a certain region in western China. The measurement results may provide useful information for the spectral detection of target in space. (Then the measurement results of it are given, which will lay the foundations of the further research of the spectral detection.)