Abstract: The relationship between the size and gray distribution of the halo in the output image of LLL(low light level) TV system and the parameters of the system was studied and a feature quantitative model of the halo was established. Firstly, the mechanism of the halo in the output image of the system was analyzed; Then, according to imaging theory, the feature quantitative method of the halo was realized by analyzing the number and the initial angular distribution of photoelectrons generated by photocathode, the movement of the photoelectrons between the photocathode and the MCP, and the collision law of the photoelectrons with non-opening wall of the MCP. Finally, the digital simulation model of the halo was built on the basis of the theories mentioned above. The experimental results show that: the results of the proposed halo effect model agree well that of experiment in gray distribution and size; the halo effect will be more obvious with the stronger of the light energy, which will generate greater impact on the imaging quality.