The study aimed at redesigning the light detection device to compensate for deficiency of existing light detection system, such as the volume, light-protection effect and so on. It adopted the reaction cup with light detection head to form a darkroom, reduced the input and output of the darkroom, and improved the effect of light-protection. It used chopping method to deduct photon background count so as to decrease the measuring error. The performance testing results showed that the photon background count of light detection device was 200 or less photon/s. The average of photometry upper limit was 1.1×107 photon/s. Coefficient of variation (C) was 3% or less, satisfying the technical requirements of the existing light detection system. It will be available for the development of precision instruments which require light signal detection, such as chemical luminescence immunity analyzer, and will be a great significance for the development of instrument industry upon light detection technique.