The invention aims at providing a cold light reflector for a natural light aging high acceleration test system. The reflector comprises a planar quartz glass substrate and a nonperiodic multilayer film which covers the surface of the planar quartz glass substrate and is composed of two high-refractive-index films of different materials and one low-refractive-index film. The reflector can reduce reflection loss of ultraviolet light radiation as well as the reflection degree of infrared light radiation so as to eliminate influence of infrared light radiation on light aging high acceleration test, and the correlation of an experiment result. The invention also provides a coating method of the cold light reflector. The method is high in controllable degree, and the optical performance of the cold light reflector is kept stable.