Abstract: First,this paper deduced the diffraction equation for refractive index phase modulation holographic grating,and pointed out that the diffraction efficiency was mainly influenced by refraction index modulation,and the diffraction efficiency of different levels came from many factors.The volume grating effect affected the diffraction efficiency of transmission hologram. This paper also discussed the factors that influenced the diffraction efficiency of scattering object,and proposed the amount of refraction index modulation was very small,the diffraction efficiency was mainly determined by chemical treatment.