The brightness is an important parameter of photometric characteristics to characterize the luminescent materials. A design method of ultra-low brightness meter was proposed, and the working principle and composition of the device were described. The automatic measurement of ultra-low brightness was realized by using the technologies of weak light signal processing, nonlinear calibration, cooling and heat dissipation. According to the principle of brightness meter measurement, the calibration was carried out, and the uncertainty of measurement was up to 5%. The ultra-low brightness meter can be used in testing sites such as laboratory and field, which can provide metrological guarantee for performance evaluation and calibration of low-level-light night vision equipment, display system, special light source and luminescent materials.