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.