Since sky-light radiation luminance is a critical parameter of atmospheric optics, it is very important for space target detection and identification. In order to acquire sky-light radiation luminance and evaluate the detection and tracking capability of optoelectronic systems for space target, a measurement system of sky-light luminance was designed and implemented. The work principles of optical signal collection and signal detection，and key techniques such as low-radiation signal detection and metrology of optical radiation used by the system were introduced. The system was applied to measure sky-light radiation luminance and the test result was analyzed. The result indicated that sky-light spectra(380nm～1100nm) could be acquired by the measurement system and more information was provided.