During practical operation, it is found that the color temperature of output flux of the fiber daylighting system with the Fresnel lens decreased severely under solar tracking error, which damages the quality of daylighting. A series of measurements on spectrum and ray tracing simulations on concentration process were designed and carried out. The data indicate that the decrease of the color temperature is a result of a chain reaction. The dispersion of the Fresnel lens, the interference of the secondary concentrator on the incident angle of the light and the attenuation characteristics of the fiber cause the reduction of the output light color temperature.