Abstract: The fluorescent screen afterglow of low-level-light(LLL) image intensifier plays a decisive role in the application of high frame rate photon counting system. According to the test method of fluorescent screen afterglow in the GJB 7351-2011 General Specification for Super Second Generation Image Intensifier , the light pulse was used as the excitation source. In this method, the illuminance of the light source dropped slowly when the light pulse excitation source stopped, which resulted in inaccurate test results in the measurement of afterglow time of short afterglow powder (μm level) and medium afterglow powder (ms level). Aiming at this problem, under the condition of continuous illumination, a test method of fluorescent screen afterglow with the voltage pulse signal of photocathode as the excitation source was proposed. In this method, the characteristics of the photocathode ultra fast response time (generally about 1 ns) and the shorter edge time (generally it can be controlled within 10 ns) of the voltage pulse signal improved the influence of excitation source time response on the accuracy of fluorescent screen afterglow test results. Based on this method, a set of fluorescent screen afterglow measuring device of LLL image intensifier was set up, and the repeatability measurement of domestic three generations LLL image intensifier afterglow of P31 phosphor powder was carried out. The error analysis of measurement uncertainty is carried out, and the expanded uncertainty is 3.2%, which reaches the accuracy requirements of traditional photpelectronic testing instrument, and can meet the requirements of afterglow measurement of LLL image intensifier fluorescent screen. The research results provide a detection method for higher performance products.