Silver/zinc selenide (Ag/ZnSe) core-shell structure spheres were made through the method of silver mirror reaction on zinc selenide micro spheres. Surface morphology of the spheres was depicted by scanning electron microscopy, X-ray diffraction and Fourier infrared absorption spectrum. This paper studies the effect of Ag/ZnSe core-shell structure spheres on the infrared absorption properties of sodium nitrate solution. The results show that, the anti-symmetric vibration absorption peaks of nitrate are blue-shifted, and the intensity are improved obviously by the effect of core-shell structure spheres.