Low light level image intensifier is an important military hardware in the night battlefield, and it usually consists of photoelectric cathodes, Microchannel Plates (MCP), fluorescent screens, and adapted dedicated power supplies. The gated power supply applied between the photoelectric cathode and MCP is an important part of the strong light protection of the image intensifier. Its main feature is the application of Pulse Width Modulation (PWM) high voltage instead of the traditional direct current high voltage, and photoelectron passes through only during the duration of the pulse, which achieves the switch operation of the electronic flow. However, domestic low light level image intensifier with gated power supply is in lack of theoretical model support and test indicators at present.Based on the above background, the theoretical models and test indicators are studied in this paper. In terms of theoretical models, this paper incorporates factors that affect the brightness of the fluorescent screen, including incident illuminance, cathode voltage, cathode pulse duty cycle, MCP voltage and fluorescent screen voltage into the model for analysis, and finally establishes an automatic brightness control model. In terms of test indicators, the two parameters of enhancer response time and stabilization time are proposed. Response time represents the time it takes from the brightness peak to 90% of the maximum brightness a high-light environment. The stabilization time represents the time between the moment when the brightness of the screen is at its highest point and the moment when the brightness is stable.Aiming to study the effect of each parameter on the response time and stabilization time of the low light level image intensifier, two variables controlled when the gated power supply is actually used are selected: cathode pulse duty cycle and MCP voltage, and the simulation analysis is carried out. By changing the step size of the variables regulation, the change trend of the brightness of the fluorescent screen in the model is calculated and analyzed, and the simulation curve is drawn to compare with the subsequent experimental results.In order to verify the results of model simulation, a fluorescent screen brightness test system is designed and produced, which includes a light source system, a signal acquisition system and an upper computer software system. The signal acquisition system uses photocells and high-speed signal acquisition circuits to collect the brightness of the fluorescent screen in real time to ensure the accuracy of the test results. Using this test system, three gated image intensifier samples based on the automatic brightness control model were tested, and the experimental results showed that the larger step size of the cathode pulse duty cycle regulation and MCP voltage regulation, the smaller the response time, but the stabilization time would increase as well; the larger step size of the MCP voltage regulation, the smaller the stabilization time, and if this parameter is too large, the brightness of the fluorescent screen will fluctuate. These trends are basically consistent with the simulation results. Besides, the low cathode pulse frequency can also cause unstable brightness oscillation of the fluorescent screen.Based on the above work, this paper verifies the feasibility of automatic brightness model, and analyzes the effect of different control schemes on response time and stabilization time, which is of guiding significance to the subsequent research on gated power supply for Low light level image intensifiers.