A mathematical model, which describes stability of imaging system, is provided. While objects consist of two kinds of brightness and have periodic structure, it is proved, that intensity of pixel on image sensor of unstable image system accords binomial distribution. So image statistical parameter can be applied to describe system velocity and image instability. In order to research the rule of image stabilization at different times, the standard deviation, which indicates discrete degree of data in statistics, is introduced as descriptive factor. Finally, the curve, which described transformation process of Pechan prism system, is given. The fluctuation of the curve is in accordance with the stability change of observed image. This conclusion proves the provided method is reasonable and effective.