The diffraction efficiency was analyzed in reflection type Hologram by use of Kogelnik's two coupled wave theory. The relationship among the diffraction efficiency, objective and reference light angles was investigated in consideration of the influence of the surrounding medium of hologram. As the result, it turns out that the surrounding medium and reference light angle have an effect on the diffraction efficiency. For example, we prepare the hologram sample that attached to glass substrate. Reference light is incident toward hologram through glass. Although the diffraction efficiency of hologram (n= 1.63) with 8 micron thickness is less than 40% on the reference light incident condition from perpendicular direction, the diffraction efficiency become more than 80% on the reference light incident condition from glass edge. This means that we can realize hologram having high diffraction efficiency even if the hologram film is thin. This suggests that edge illumination is effective in using reflective hologram and have merit on manufacturing process, even if the hologram film is thin.