The variation law of the performance with working time in the super Gen-II image intensifier was studied, and the characteristics of the performance variation were grasped. Through performance testing and curve fitting, it was found that the brightness gain and signal-to-noise ratio gradually decrease with working time, and the resolution remains almost unchanged with the change of working time. In addition, the brightness gain changes exponentially with working time. That is, when the working time is within 10,000 h of the super Gen-II image intensifier, the brightness gain changes rapidly with the working time; however, as the working time increases, the brightness gain decreases and finally stabilizes. The signal-to-noise ratio changes as a polynomial function with working time and finally stabilizes. The signal-to-noise ratio changes as a polynomial function with working time and gradually decreases with working time. Through anatomical analysis of the image intensifier after working for a long time, its brightness gain and signal-to-noise ratio changes were found to be mainly related to the sensitivity of the photocathode, luminous efficiency of the phosphor screen, and gain stability of the MCP. Compared with the sensitivity and luminous efficiency of the fluorescent screen, the MCP gain stability changed significantly.