Abstract: The number of space debris is growing in recently years, and it poses grave threats to the security of spacecrafts. In order to manage the risk, it is of vital importance to obtain the position information of space debris and spacecrafts by observation and therefore provide pre-warning service. The Ground-Based Electro-Optic Telescope has absolute advantages in terms of observing the GEO region. In this paper, we get the minimum detectable size of debris by using simulated formula based on signal to noise ratio theory and then use observational tests to verify the computational formula. After analyzing the influencing factors of detection ability and comparing its debris detection ability of the GEO region in two observation modes, we get the quantitative relation between aperture size and exposure time. This paper can provide some reference to devices designed for space debris detection.