Abstract: Visible light imaging detection of electro-optic (EO) system plays a key role in space-object detection. How to detect space-object in strong background luminance has always been a choke point in limiting EO system's detection ability. The primary specification for expressing detection ability is signal- to-noise ratio(SNR). Based on analysis of the effect factors, a calculation formula of detection ability and the fundamental of detection probability were derived. The influence of the sky strong background luminance on the detection ability was analyzed, and the SNR of EO system versus spectral filtering mode and different observation stations were given in the paper. The theoretical results show that the detection ability of EO system can be improved, increased by 100 percent, through the propriety spectral filtering technology. The detection probability is increased by 45 percent (from 51 percent to 96 percent) through changing the observation station of EO system. Theoretical results fit with the experimental research.