The sky background brightness has been measured with sky background brightness measurement equipment in desert region of northwest china, the spectrum distributing of background brightness of the region is researched, and the detecting ability of the Electro-Optical system is also researched and simulated through the filtering technology in the region under the spectrum distributing. The research results indicate that the background spectrum distributing is obvious different to the theory spectrum, the proportion of the 600～900 nm band is bigger relative to theory, and it varies slowly with the variety of azimuth angle and zenith angle. The detecting ability can only improve 0.1 magnitude through filtering technology when the background brightness is 10 W·m-2Sr-1.