Putting the AgCl nanoparticle as crystal nucleus and in the condition of the existence of tri-sodium citrate, the Ag+, which covers the surface of AgCl nanoparticle, photochemically reduces to Ag and thus Ag/AgCl composite nanoparticle is obtained. The spectroscopic characters of Ag/AgCl nanoparticle in aqueous solution have been studied. There are two resonance scattering peaks at 310 and 590 nm, and an absorption peak at 400 nm.