The main difficulty of star detection during daytime is the over strong background radiation. Detectors with three same parameters are rigid connected to the detection platform by an all-weather near Infrared multi-FOV detection system to detect stars. According to geographical positions in China, star background contrast during daytime at near Infrared band in three detection FOV changing with sun zenith, platform azimuth, pitching angle in x and y direction as well as platform height is analyzed. The results show that with the variation of sun zenith, contrast similar exponent increases. With the variation of platform azimuth, the contrast approaches to normal distribution. When the platform has a certain pitching angle, the contrast changes little and change range is small, but three FOV has a big difference such as from 1.5 to 20 times. The contrast will exponentially increase greatly with the platform height changing to provide a better basis for star magnitude amendment.