Abstract: The limiting magnitude of an electro-optical system can be improved through the spectral filtering technology in daytime space target observation. Considering the characteristic of spectral filtering and the inconsistent responses to different wave bands, the precision of magnitude measurement for spectral filtering technology was analyzed based on the measurement method in exist, and a correction method was given. The magnitude of a space target was measured by an electrooptical system based on the measurement way in existence and the result was simulated through the correction method. The two results were analyzed comparatively, proving that the spectral filtering can improve the detecting ability at the expense of precision deterioration (0.5 magnitude at most)．