Abstract: To comprehensively evaluate the performance of a UV image intensifier, a testing apparatus was established for measuring the signal-to-noise ratio of the UV image intensifier assembly. First, according to the working principle of the UV image intensifier and the method used to test the SNR of the low-light-level image intensifier, the incident radiation power required to measure the SNR of the UV image intensifier was calculated. Second, based on the measurement of the ultraviolet wavelength parameters, a method for testing the signal-to-noise ratio (SNR) of the UV image intensifier with a small-spot imaging detection is proposed. Subsequently, based on the detection method of small-spot imaging for determining the radiation intensity, an SNR measurement device was established for the UV image intensifier, and the measurement uncertainty of the device was analyzed. Finally, the SNR of the ultraviolet image intensifier was measured using a calibrated test device, and the measurement repeatability was high. The results showed that the uncertainty of the UV image intensifier SNR test device based on the detection method of small-spot imaging with the determined radiation intensity was 13.3%, the SNR of the UV image intensifier was 15.3, and the repeatability deviation of the SNR was 2.86%. This satisfies the measurement requirements of UV image intensifiers with a high SNR in ultraviolet alarms and other application scenarios.