Abstract: In order to reveal the influence of the voltage variation of microchannel plate on the signal-to-noise ratio of LLL image intensifier and optimize the performance of the image intensifier, the curves that the signal-to-noise ratio of super Gen II and Gen III image intensifiers variates with the voltage of a microchannel plate were obtained by the aid of a signal-to-noise ratio tester. As for the super Gen II image intensifier, when the microchannel plates voltage is in the range of 600～800V, the signal-to-noise ratio is monotonically increased to 25.9, when it is in the range of 800～900V, the ratio is 25 or so and has downtrend, and when 900～1000V, the ratio is rapidly decreased to 21.8. As for the Gen III image intensifier, when the microchannel plates voltage is in the range of 800～1000V, the signal-to-noise ratio is monotonically increased to 27.87, and when the voltage is in 1000～11800V, the ratio fluctuates from 26.61 to 28.66.In combination with the theoretical analysis of microchannel plates noise factor, a method to reduce the noise factor of microchannel plates and improve the signal-to-noise ratio of LLL image intensifiers is proposed.