Using the closed orbit theory,we study the classical motion and calculate the photoabsorption spectra of Rydberg hydrogen atom between two parallel metallic surfaces.The results show that the metallic surfaces have a significant effect on the photoabsorption process.When the distances between the hydrogen atom and the two metallic surfaces are close to a critical value dc,the number of the closed orbits is the greatest.When the distance larger or smaller than dc,the number of the closed orbits decreases and the absorption spectra are shown to exhibit a damping oscillation.This work is an interesting new application of closed-orbit theory and is of potential experimental interest.