ZnO nanoparticles in porous anodized alumina were fabricated by sol-gel method. The PL spectra of pure ZnO nanoparticles, porous alumina template and the ZnO/PAA composite system were investigated after annealed at different temperatures. The annealing of ZnO/PAA composite system displays very complicated behavior, where changing of luminescence intensity and a "red shift" of emission frequency were observed at less or higher than 500 ℃ of the annealing temperature, respectively. To explain the phenomenon, it is considered that the emission origin of the green luminescence of ZnO nanoparticles came from OZn. It is suggested that the ZnO/PAA composite system should be annealed at the temperature above 500 ℃ in order to get intense luminescence of ZnO nanoparticle.