Abstract: The key technology of space target detection was studied during daytime, including analysis of atmospheric transmittance, sky background radiation measurement, detection ability calculation. Infrared K band spectrum was applied to the 1.23 m large aperture telescope to verify the key theoreties. Experiment shows that after optimization the limit detection of infrared optoelectronic system is 10.38 magnitude at 30 pitching angle and the detection ability increases 24.9% than before optimization. This research has a positive significance for mid-high orbit satellite detection throughout the day.