Abstract: To achieve the large dynamic range and highprecise test for the cutoff depth of the outband of solar blind untraviolet(UV) filters, a system which not only used xenon lamp with a monochromator as the standard light, but also used photon counter as the detector was proposed. Additional, the error of the system was analyzed. The major equipments were the xenon lamp with a monochromator, the standard reflective neutral attenuator and the single photo counter. Based on the substitution method the measurement was carried out. The photo counter detected the number of the xenon lamp through the attenuator as the reference to substitute the initial photo number of xenon lamp, then the cutoff depth of filters could be acquired. Results show that the test system can extend the testing dynamic range of filter optical density to 0~-11OD, it realizes the continuous measurement the visible spectral bands at 1 nm intervals, and greatly reduces the test error of the system.Compared with the test system using narrow band LED as the light source, the test uncertainty reduces from 2% to 0.5%,and the relative repeatability error is from 0.2% down to 0.13%.