The Bragg-shift in reflection-type photorefractive holographic gratings, especially its time evolution, has been investigated both theoretically and experimentally. Experiments demonstrated that there does exist the Bragg-shift in reflection-type photorefractive holographic gratings, and it increases with time similarly to the time evolution of the index modulation. The research shows that in large-scale holographic storage, the influence of Bragg-shift on the reconstruction quality can be negligible so that the hologram can be read out at the same angle as it was recorded, if the hologram was recorded for a short exposure time.