To complete the quantitative analysis of the solar-blind ultraviolet corona signal, a time-domain diffuse round-spot photon-counting algorithm is designed to analyze the image collected by the imaging system. First, the principles of single-photon detection and photon counting are described; second, an imaging detection system based on solar-blind ultraviolet ICMOS is designed. To meet the afterglow response of the screen, the CMOS driver is optimized to make the frame rate up to 390 fps. Then, by analyzing the traditional connected domain photon counting algorithm, a diffuse round spot photon counting algorithm based on the time domain is proposed, and experiments show that the algorithm designed in this study has higher accuracy than the traditional technical algorithm. Finally, through an experiment with an ultraviolet lamp source, it is verified that the designed photon counting algorithm can be implemented in the hardware of the imaging detection system, and the counting effect is good.