It was realized that the erasable holographic storage in the visible range for the thin layers of PMMA matrices doped with N-salicylideneaniline material. An argon laser beam of 488.0 nm and a He-Ne laser beam of 632. 8 nm were used as writing and reading light, respectively. The intensity of the diffraction signal increased with the increase of writing time, then it decreased with the increase of writing time. In the grating growing and dropping process, the relation between erasing time and grating diffraction signal was studied. For the former, the diffraction signal increased firstly, then decreased with the increase of the erasing time; for the latter, a decrease in the intensity of the diffraction signal was observed. A possible explanation is that pressure-driven mass transport induced from photoisomerization which causes a change on the surface to form a surface-relief grating. However the surface-relief grating partly counteracts the phase-grating because of the two gratings with a phase difference of π.