Abstract: Modulation transfer function (MTF) and noise of EBS-CCD are analysed. The detective equation of EBS - CCD at low light level is established based on the concept of signal to noise ratio transfer function (SNTP). The values of detectivity of EBS - CCD at low light level under several different conditions are calculated based on the image detective equation of EBS - CCD. Theoretical calculating results well coordinate with the experimental results. Some ways of improving detective ability of EBS-CCD are proposed.